SEL4@ll program for social and emotional development among European adolescents: a study protocol for a randomized controlled trial

Abstract

Background

Rapid global, social, economic, and technological changes are exposing children and adolescents to unprecedented pressures during a critical developmental stage. To help them adapt to the complexities of the modern world, education must extend beyond academic achievement and intentionally foster key competencies such as social and emotional skills. Grounded in the frameworks of Social and Emotional Education (SEE), character development, and positive youth development, the SEL4@ll programme introduces an innovative school-based intervention delivered through a serious game. This digital approach integrates pedagogical theory with motivational game design to promote socio-emotional learning in an engaging and inclusive format. The present study aims to design, implement, and evaluate the SEL4@ll intervention across European schools to enhance students’ social-emotional competencies, scholastic well-being, and social inclusion.

Methods

This randomised controlled trial will evaluate the effectiveness of the SEL4@ll programme among approximately 1,000 students aged 10–16 years from schools in Germany, Italy, Spain, and Finland. The intervention combines six weeks of individual gameplay with teacher-facilitated classroom sessions. Quantitative data will be collected at baseline (T1), post-intervention (T2), and two-month follow-up (T3) to assess primary outcomes (social-emotional competence) and secondary outcomes (student well-being and social inclusion). Qualitative data from students and teachers will complement these findings to explore user experiences and contextual factors. Analyses will employ linear mixed-effects models to account for clustering and intercultural variability.

Discussion

The SEL4@ll program represents an innovative effort to integrate digital serious gaming with social and emotional education across European. The cross-national design allows for the assessment of cultural adaptability and generalisability of a shared SEE framework, contributing valuable evidence on how digital interventions can support well-being and social inclusion in diverse educational contexts. Findings from this study will inform the development of scalable, evidence-based strategies for promoting emotional resilience, empathy, and positive youth development through technology-enhanced education.

Trial registration

The clinical trial is registered at ClinicalTrials.gov (Identifer: NCT07093645, date assigned: July 2025).

Supplementary Information

The online version contains supplementary material available at 10.1186/s40359-025-03678-w.

Background

The rapid global, social, economic and technological changes occurring in the world today are exposing children and adolescents to unprecedented pressures and challenges during a vulnerable stage of their lives [1–4]. As a result, many students enter school already struggling with serious socio-emotional difficulties, which negatively impact both their academic performance and psychological well-being [5, 6]. Multiple risk factors such as poverty and social inequality, bullying and cyberbullying, conflicts and changes in family structures, addiction to technology and social networks, academic stress and burnout, as well as loneliness and social exclusion, create a challenging environment that compromise healthy development and psychosocial adjustment [7–14].

To address these challenges and facilitate children’s and adolescents’ better adaptation to the complexities of the modern world, education must follow an alternative approach that goes beyond academic performance and intentionally promote the development of key competencies such as social-emotional skills [15–17]. These skills enable children and adolescents to better understand their own and others’ emotions, express and regulate their feelings, establish healthy and empathic relationships, collaborate with others, resolve conflicts constructively, and make responsible and ethical decisions. This is particularly relevant for students experiencing socio-economic or other disadvantages, as they benefit from developing such key competencies in self-awareness and emotional regulation to help reduce inequities in both social and academic settings [18, 19].

Schools provide a natural and inclusive context for learning social and emotional skills, but there are different models that vary in the types of competencies and how they should be taught. Cefai and Cavioni’s model of social and emotional education (SEE) [20] proposes an integrative approach that combines six key perspectives for child and adolescent well-being: social and emotional learning [21], positive education [22], mindfulness [23, 24], resilience [25, 26], inclusive education [27, 28] and supportive communities [29, 30]. This model aims to develop intra- and interpersonal competencies that strengthen self-awareness, self-regulation, social awareness and social regulation, along with resilience and academic learning skills, which are essential to meet the social, emotional and educational challenges of a changing world [19].

There is growing evidence that SEE can improve positive academic attitudes and higher academic achievement, increase prosocial behaviour, and decrease antisocial behaviour, anxiety, depression and suicide [31–34]. More generally, it contributes to harmonious school relationships, social cohesion and inclusion, positive attitudes towards individual and cultural diversity, and an overall level of well-being [35, 36]. SEE might also play a central role in promoting character development in children and adolescents, which emphasizes the cultivation of self-direction, cooperativeness and self-transcendence as essential dimensions for personal growth and social integration [37]. These character dimensions can be considered as an indicator of personal maturity and align with the broader model of positive youth development proposed by Oliva Delgado [38], which outlines the interplay of personal, cognitive, emotional, social, and moral assets that give support and experiences needed for resilient and well-adjusted youth. By linking the socio-emotional competencies emphasized in SEE with the character strengths identified by Cloninger and the multidimensional areas of youth development outlined by Oliva Delgado, a comprehensive model emerges that situates academic and psychosocial outcomes within a wider developmental context. Thus, SEE interventions not only strengthen students’ emotional and social competencies but also lay the building blocks for long-term psychological well-being, constructive social integration, and flourishing across the different domains of adolescent development.

Promoting the socio-emotional development of students has therefore become a priority for educational institutions in Europe and beyond [39] To achieve this goal, SEE programmes that involve the whole school community have been implemented and their effectiveness has been demonstrated for students from different age groups [40–42] and with different circumstances, including students with disabilities and special educational needs [43, 44]. However, challenges in implementing SEE programmes remain, including intervention quality, limited teacher training and insufficient evidence of long-term effects [45–47].

Digital tools including educational apps, videogames and artificial intelligence have been developed and incorporated into the intervention framework by providing interactive and engaging platforms [48–50]. Thus, an innovative way to deliver SEE interventions is using serious games, which facilitate the development of skills or knowledge combining pedagogical theories and motivational principles of game design with an educational objective [51–53]. Serious games can immerse students in realistic social scenarios through game-based missions and challenges to develop their social-emotional skills such as empathy, teamwork and conflict resolution [54, 55]. Initial evidence suggests they can improve motivation and learning processes, but further evidence from randomised controlled trials is needed to demonstrate their effectiveness, scalability and cultural adaptability [48, 56].

Aims

The present trial addresses this gap through the project Promoting well-being among European adolescents- an inclusive and digital programme to strengthen socio-emotional competencies (SEL4@ll), which combines SEE with digital intervention through a serious game. This study aims to design, implement and evaluate a serious game for European children and adolescents aged 10–16 years to promote their socio-emotional competencies, scholastic well-being and social inclusion. The study hypothesis is that students participating in the programme will show an improvement in these outcomes compared to the students in the control group.

Methods

Trial design and setting

The study design is based on a quasi-experimental approach within the framework of a randomised controlled trial with mixed methods (see Fig. 1). In the quantitative part, a longitudinal design with an experimental group (participating in SEL4@ll program) and a control group (standard school curriculum) is implemented. Data will be collected through online surveys at three measurement points: at baseline before intervention (T1), at post-treatment immediately after the six-week intervention (T2) and at follow up two-months later (T3). The specific aim of quantitative approach is to determine the effectiveness of the SEL4@ll intervention in primary outcomes, which relate to the development of participants’ social and emotional competencies, as well as secondary outcomes such as student well-being and social inclusion.

Fig. 1.

Study design of SEL4@ll intervention

The qualitative part includes focus groups and individual interviews with students at different time points during the design, programming (alpha, beta, soft launch and final launch) and implementation phases. The qualitative data collection will serve to develop the serious game based on the students’ needs and preferences as well as to capture their satisfaction and subjective playing and learning experiences. In addition, feedback interviews will be conducted with teachers to explore their experience during the implementation and to identify potential barriers. Qualitative and quantitative data relating to the primary outcomes and effectiveness of the intervention will be considered together in the final phase of the study.

A particular focus is on the intercultural comparability of the results, as the study is being conducted in primary and secondary schools in four European regions: Mecklenburg-Vorpommern (Germany), Umbria (Italy), Valencia (Spain) and Jyväskylä (Finland). This will determine the adaptability of the intervention to different cultural and school settings within the Europe.

Therefore, a sample of children and adolescents from these four regions who are in transition from primary to secondary school, aged between 10 and 16 years will be assessed. The selection follows the recommendations of the Standard Protocol: Recommendations for Interventional Trials statement SPIRIT [57].

Participants

Children and adolescents between 10 and 16 years of age, generally corresponding to grades 5 and 6 of primary school and grades 1 to 4 of secondary school, are eligible to participate in this study. They need the written consent from a parent or legal guardian. Another requirement for participation is that students must attend school regularly and complete the survey at all three measurement points (baseline T1, post-treatment T2 and follow-up T3).

Exclusion criteria will be: (a) Students without parental or legal consent, (b) students who are unable to adequately understand or complete both the assessment and intervention due to significant cognitive, developmental or language impairments, (c) students who are absent for a prolonged period during the implementation phase, for example due to illness or a change of school, (d) students who are participating in another intervention at the same time that targets similar areas of development and which could therefore compromise the results.

Conditions of participation for schools include hosting a two-hour training seminar for teachers before the intervention. Schools must provide the necessary settings for data collection, both for the qualitative part (rooms for focus groups and interviews) and for the quantitative part (computers or tablets for online surveys). They also help with communication with parents and legal guardians and take on the task of obtaining informed consent. Finally, they are responsible for implementing the intervention protocol in the selected classrooms in accordance with the specifications and under the supervisions of the local research group.

Participant timeline

The SEL4@ll project began in 2023 with a systematic review of the literature on SEL to establish a theoretical framework for the intervention. Based on this foundation, the research team designed the psychological content and developed the serious game on a digital platform called Unity. Between late 2024 and early 2025, several test versions of the serious game (alpha, beta and soft launch) were piloted with small student groups and critical friends. Their feedback on both content-related issues and technical bugs was used to continuously refine the serious game.

The main study trial is scheduled from January until April 2026 (see Fig. 2). The recruitment of participating schools in the four regions (Germany, Italy, Spain and Finland) took place from September and will be completed by December 2025. During these months, the research team met with school leadership, presented the SEL4@ll program, and secured the necessary permissions from schools and local authorities. Informed consent was also collected from students and their parents or guardians. In preparation for the intervention, teachers were offered training sessions where the SEL4@ll program objectives, the serious game, and the accompanying didactic materials were introduced. Video-tutorials and a set of FAQs were provided to support implementation.

Fig. 2.

Study timeline for SEL4@ll program

The first assessment (T1) will be administrated through an online survey during school hours, the same week when the intervention starts. The intervention itself will run for six weeks. During this period, students will play the serious game individually either on a computer (keyboard navigation) or tablet (touchscreen), which they can access via any web browser. At school, weekly follow-up sessions will be held, where teachers facilitate activities from the digital didactic materials and monitor the student’s progress. At the end of the six-week intervention, students will complete the second assessment (T2) through the online survey. In addition, qualitative data from both students and teachers will also be collected at this stage to capture user experiences. The results of these assessments will guide the final revision of the serious game before its final launch in December 2025.

Two months after the intervention has been finished, a third and final assessment (T3) will be conducted with students though an online survey to evaluate follow-up effects. Students in the control group will complete the same three assessments (T1-T3) during the same period but will gain access to the SEL4@ll program only after the final launch and the trial has been completed.

Recruitment

Recruitment is carried out in close cooperation with schools in the four participating countries (Germany, Italy, Spain and Finland) to achieve the desired sample size. Formal partnerships are established with primary and secondary schools, and recruitment takes place at school level rather than on an individual basis to ensure that entire groups of students can participate together. This strategy minimises selection bias, simplifies logistics and increases participation rates. Teachers play a key role in recruiting and retaining participants. Preparation meetings and training sessions are held to familiarise them with the SEL4@ll programme so that they can motivate and support students throughout the intervention. Continuous communication with schools ensures smooth organisation, enables participation to be monitored and any concerns to be addressed promptly, thereby reducing the risk of dropouts.

Sample size

According to Eurostat [58], the number of children and adolescents aged between 10 and 16 years in the European Union is around 25–30 million. With a confidence level of 95% and a margin of error of 5%, the representative sample size would be 385 participants. However, the aim is to reach at least 1.000 students for the overall sample, 500 students in the intervention group and 500 students in the control group. Participants are organised by class and school, therefore, allocation to the control group and the intervention group takes place at school level. These are randomly assigned by the research team to the respective group using computer-generated random numeric TAN codes. The assignment sequence is computer-generated using a specially developed application. The natural gender distribution within each participating school and class will be preserved, ensuring that both groups reflect the actual proportion of boys and girls in the population.

Interventions

The intervention group participates in the SEL4@ll program, which consists of a self-guided serious game that students play individually during six weeks alongside regular school lessons to enhance their social-emotional competencies. The serious game is hosted on an online platform accessible via any web browser and available in five languages (German, Italian, Spanish, Finnish and English). The intervention is accompanied by weekly follow-up sessions with their teachers, who facilitate activities using complementary didactic materials at their disposal. These sessions help the students to reflect on and consolidate the skills trained in the serious game. The program is based on the theoretical model of social and emotional education (SEE) [20, 59] and personality development [37] and targets the multidimensional domains of positive youth development, including personal, cognitive, emotional, social and moral domains [38]. The overarching goal is to improve adolescents’ academic well-being and social inclusion by teaching important life skills [60].

In the serious game, players embark on an adventurous journey with the aim of restoring balance to the planet and the school. To do so, they should develop key competencies and skills, which reflect their potential and inner strength. To acquiring these skills, players must cross through magical gates located at a school setting, and complete interactive prosocial challenges, becoming socially and emotionally competent individuals who take responsibility, find meaning and joy in life and strive for a just society. A “dark force” stands in their way, which feeds on conflict and inequality, spreading everywhere and infecting everyone.

The serious game is divided into five main missions, which are represented by five magical gates (see Fig. 3). Players must discover and pass through these gates to learn the required skills to defeat the influence of the “dark force”. Each gate is linked to specific social and emotional skills and represents its own area of positive development. The order in which the gates are entered is freely selectable. This allows adolescents to develop their skills flexibly and according to their individual needs and preferences. At the same time, it ensures that social, emotional and prosocial skills are not taught in isolation, but are integrated into a dynamic process of personality development across all central areas of life. Once the first four gates have been successfully completed, the last gate appears, opening access to the final mission, in which the player must confront the “dark force”.

Fig. 3.

Images from the serious game SEL4@ll and its different missions/gates

More specifically, the Gate of Self leads deep into the core of the planet, where the focus is on personal development and fostering self-confidence and sense of meaning in life, resilience, and leadership skills. Here, players navigate a labyrinth of caves with enchanted crystals and face magical mirrors to discover their true self. First, players should recognize irrational beliefs and what gives them purpose in life. Second, players dialogue with harmful inner voices to overcome their personal difficulties by turning them into allies. Thirds, players need to prevent conflicts by reflecting on the consequences of their actions, which ultimately shapes both personal destiny and the collective well-being of others.

The Gate of Knowledge leads to a world of art and science where disciplines that were once united are now fragmented and divided. This gate is focused on cognitive development and aims to promote self-motivation, growth mindset, flexibility and critical thinking. Players first explore their surroundings, the different disciplines are presented as different buildings and are rejected by all disciplines until they find the transversal discipline (building) of critical thinkers. Here, players will find the keys that grant them access to the buildings of art and science, but this requires the use of goal setting, self-regulation, persistence and problem-solving. To reunite the disciplines, players must collect fragments of truth, analyse them and connect them with one another. Together, these fragments form the “puzzle of humanity”. They are accompanied by a robot that helps them to use their creativity and cognitive flexibility in a targeted manner. This illustrates the idea that intellectual growth requires both perseverance and adaptability – and that the search for truth is not only a personal responsibility, but always a collective one as well.

The Gate of Emotions leads players into a decaying city where they must face a series of emotional challenges. The focus here is on emotional development and the cultivation of emotional intelligence, empathy and compassion. To advance, players must recognise, interpret and regulate their own emotions and others. In doing so, they acquire emotional knowledge and learn various ways to better navigate even complex emotions. The path leads players through dark and abandoned alleys until they reach the city centre that has grown into a bright and green oasis. Here they meet a wise owl which teaches them compassion and mindfulness. At the end of their journey, players realise that the path through life can be difficult, but that emotions are valuable allies to find their own way.

The Gate of People leads to a foggy swamp inhabited by creatures called Maligores, and players must get themselves to safety. The focus here is on social development and is designed to promote skills such as communication, gratitude and positive influence. Initially, players must help combat three social dilemmas, which underscore the need for solidarity and mutual support: hunger, social exclusion and inequality. After, they will find the House of People, where they meet a wise couple who teach them to question their initial assumptions about others while engaging in prosocial problem-solving. The people have created the Wall of Gratitude, which allows the players to realize the important things in life, and remember where they can find support such as family, school, and community. As the game progresses, players realise that the Maligores are not necessarily enemies. They are misunderstood beings, emphasising the value of perspective-taking and relationship skills.

In the Final Gate, players face the dark force and must use the social and emotional skills they have acquired throughout the serious game. The mission focuses on moral development and addresses equality, responsibility and justice. Chasing after the dark force, players must rely on the help of others to navigate their way through deceptive traps, brain teasers and tricky tasks to reach the lair of the dark force. Here, participants discover a treasure guarded by the dark force, which contains all the good ideas and values that humanity has neglected. The challenge is to decide whether and how to raise the treasure, as every decision has consequences. This final mission forces players to tackle ethical dilemmas and consider the far-reaching implications of their decisions for restoring their skill tree and balance to the world.

In addition to the five gates, there are so-called mini-quests scattered across the various locations in the game. These serve to promote prosocial behaviour and put newly acquired skills into practice. In these mini-quests, players meet non-playing characters (NPCs) who need assistance, for instance a classmate who forgot their lunch money, a neighbour who has lost their parrot, or the younger sister who a has trouble with their homework.

The serious game has all the typical video game features such as scoring, rewards through badges, skill tree and leaderboards. These features, the captivating story of the serious game, the gradual unlocking of missions and positive reinforcement within the game (expansion of the skill tree) are designed to keep the students engaged. Furthermore, the weekly follow-up sessions serve not only to reinforce learning but also to keep students motivated. In addition, students and teachers discuss any difficulties or bugs that will be forwarded to the research team. The research staff monitor progress through anonymised backend analyses, tracking mission completion, time spent playing and frequency of logins. This data is reviewed weekly and forwarded to teachers so that they can encourage students to increase their playtime if participation is low.

However, if students feel uncomfortable, if their parents revoke their permission, or if teachers observe negative effects (e.g., emotional distress, intense competitive pressure), participants may withdraw from the intervention at any time.

In the meantime, the control group continues with the regular school curriculum without additional interventions. To ensure equal learning opportunities, they will be offered the SEL4@ll program in the following trimester. This delayed implementation not only provides a fair comparison between groups but also guarantees that all students ultimately benefit from the social and emotional learning activities.

Outcomes

Primary and secondary outcomes will be measured at three moments: baseline prior to the intervention (T1), post-treatment immediately after the six-week intervention (T2) and at two-months follow up (T3). At each moment, students will complete an online survey, which includes self-report questionnaires on social and emotional skills, school well-being and social inclusion. To complete quantitative measures, qualitative data will be collected at T2 from students and their teachers.

Primary outcomes

Social and Emotional Competence will be measured with several established instruments.

1. The Social Skills Improvement System Social and Emotional Learning Brief Scale (SSIS SEL Brief; [61]) is a 20-item self-report tool which covers five domains that align with the CASEL framework [21]: self-awareness, self-management, social awareness, relationship skills, and responsible decision-making. Items are rated on a 4-point Likert scale from 1 (Not True) to 4 (Very True), with total scores ranging from 20 to 80. Higher scores indicate stronger perceived SEL. The instrument has been adapted into different languages and consistently demonstrates excellent psychometric properties [62].

2. The Emotion Regulation Questionnaire (ERQ; [63]) assess the use of two emotion regulation strategies, cognitive reappraisal and expressive suppression. The measure consists of 10 items which are rated on a 7-point Likert scale (1 = Strongly disagree, 7 = Strongly agree). Higher scores indicate more frequent use of the respective strategy. The ERQ has been extensively applied across cultures, with evidence of validity and reliability [64–66].

3. The General Self-Efficacy Short Scale (ASKU; [67]) comprises three items that are rated on a five-point Likert scale from 1 (Does not apply to me at all) to 5 (Completely true). Higher scores indicate greater self-efficacy. Research supports the scale’s reliability, factorial validity, and cross-national invariance [68].

4. The OECD Survey on Social and Emotional Skills (SSES, [69]) measures a variety of social-emotional skills, including open-mindedness and persistence. Open-mindedness is assessed with 24 items distributed across three subscales: tolerance, curiosity, and creativity (8 items each). Persistence is assessed with three items. All use a 5-point Likert scale (1 = strongly disagree, 5 = strongly agree), with higher scores indicating higher levels of each respective skill. Reliability, construct validity, and cross-cultural invariance of the SSES scales have been well documented [70].

Secondary outcomes

Student well-being will be measured using two indicators.

1. The Student Well-Being Questionnaire (SWBQ; [71]) comprises 19 items rated on a 6-point Likert scale (1 = never/disagree, 6 = very often/agree). It covers three positive dimensions of student well-being (positive attitudes toward school, enjoyment in school, positive academic self-concept) and three negative ones (worries in school, physical complaints in school, and social problems in school). Higher scores on positive dimensions reflect better well-being, whereas higher scores on negative dimensions reflect poorer well-being. Reliability of the subscales has been confirmed in multiple studies [72, 73].

2. The School Burnout Inventory (SBI; [74]) includes 9 items measuring three dimensions: exhaustion at school, cynicism toward the meaning of school, and sense on inadequacy at school. Responses are given on a 6-point Likert scale (1 = completely disagree, 6 = completely agree). The SBI has been validated in numerous languages with robust psychometric evidence [75, 76].

Social inclusion will be assessed through the Perception of Inclusion Questionnaire (PIQ; [77]). It consists of 12 items rated on a 4-point Likert scale (1 = Not at all true, 4 = Certainly true). It measures three key aspects of students’ social inclusion at school: emotional self-inclusion (feeling accepted and valued), social inclusion (feeling part of the peer group), and academic self-concept (perception of one’s own academic competence. Each subscale ranges from 4 to 16 points; the total score ranges from 12 to 48. Higher values indicate stronger perceived social inclusion. Previous studies confirm the PIQ’s reliability and validity [78–80].

Qualitative data collection

Qualitative Interviews will be conducted with students and teachers using different formats.

1. Focus groups with 10–15 students will be conducted after the intervention to explore their experiences with the game and the learning activities. Students will be invited to share and discuss what effect, affect and impact the intervention had on them, for instance, what they have enjoyed, what they found less engaging, or what they think they have learned.

2. Individual interviews will be conducted with students individually to provide deeper insights into how students perceive the impact of the serious game on their social and emotional skills, well-being, stress management, sense of inclusion, and creativity.

3. Feedback interviews with teacher will be conducted to ask about their experience using and adapting the didactic materials in class, as well as their observations of students’ motivation, challenges, and progress during the intervention. This feedback will be used to further refine and improve the SEL4@ll program.

Data management

Outcome, baseline, and additional trial data will be collected from participating students in the SEL4@ll program (experimental groups) and from students in control groups in schools located in Germany, Italy, Spain, and Finland.

Data will be gathered at baseline (T1) before the intervention and at post-intervention (T2), and follow-up (T3) after about a month of completing the SEL4@ll program.

Standardised digital questionnaires (hosted on a secure online survey platform; e.g., LimeSurvey/EvaSys) will be used to assess the variables of interest. To promote data quality, assessors and local school contacts will receive standardised training and written guidance on administering surveys and ensuring independent, undisturbed completion by students. Automated range and consistency checks will be implemented within the digital survey system (e.g., preventing impossible values or missing key variables). Participant retention will be promoted by close collaboration with participating schools, reminder communications, and flexible survey administration windows.

All collected data will be stored pseudonymised using unique study IDs. Person-specific information (e.g., class lists, consent forms) will be stored separately and securely at each national site in compliance with General Data Protection Regulation (GDPR).

Electronic data will be hosted on secure university servers with access restricted to authorised research staff. Data entry and coding will follow a predefined data dictionary. Automatic data validation rules (e.g., range checks, logical cross-checks) and random manual audits will ensure high data quality.

Statistical methods

Primary and secondary outcomes will be analysed using linear mixed-effects models (LMMs) with random intercepts for classes and/or schools to account for clustering and country-level variation. The main fixed effect will be group allocation (SEL4@ll intervention vs. control). Models will include baseline values of the respective outcomes as covariates, and additional student-level or school-level covariates (e.g., age, gender, school type) may be considered if theoretically justified.

Missing outcome data will be addressed under the assumption of missing at random (MAR). Depending on the proportion and pattern of missingness, we plan to use multiple imputation or full-information maximum likelihood (FIML) within the LMM framework. Furthermore, exploratory subgroup analyses (e.g., by country, gender, or baseline SEL score) and adjusted models (including socio-demographic covariates) will be conducted. A detailed statistical analysis plan (SAP) will be finalised prior to database lock and made available upon reasonable request.

Qualitative data will be analysed using an inductive thematic analysis approach [81] in two main steps. First, two team members will independently code each focus group transcript, identifying descriptive categories until data saturation is reached. Second, the team will discuss and organize these categories into a hierarchical structure, reaching consensus on final themes. Findings will be integrated with quantitative data to provide a comprehensive understanding of the intervention’s effectiveness and implementation process, allowing triangulation of outcomes across multiple sources and perspectives within the broader mixed-methods framework.

Data monitoring

Given the low-risk, school-based nature of the SEL4@ll intervention (non-clinical, educational program), no independent Data Monitoring Committee (DMC) will be established. The study team, coordinated by Frances Hoferichter, Konstanze Schoeps, and Annalisa Morganti will oversee data integrity and safety monitoring internally. This approach is considered adequate because the intervention poses no known health risks and consists of educational content only.

No interim analyses for efficacy or futility are planned, and no formal stopping rules are defined. The trial will continue as planned unless unforeseen ethical or safety issues arise.

Although no physical or medical risks are expected, any adverse events or unexpected negative effects (e.g., psychological distress reported by students) will be documented by local school contacts and communicated to the study coordination team. Serious adverse events, should they occur, will be reported to the relevant institutional review boards/ethics committees.

Formal external auditing of trial conduct is not planned, as the project is an educational, non-clinical intervention with minimal risk. Internal monitoring of protocol adherence and data security will be performed by the coordinating institution.

Ethics and dissemination

The study was reviewed and approved by the ethics committees of the University of Greifswald (reference number: BB 127/24a) and the University of Valencia (reference number: 2024-PSILOG-3715935). In contrast, the ethics committees at the University of Jyväskylä and the University of Perugia indicated that a formal ethical pre-review was not required under their institutional guidelines and that an ethics statement would be provided after conducting the trail study. All data will be processed in accordance with the General Data Protection Regulation (EU) 2016/679 (GDPR) and relevant national data protection laws.

A coding system specially developed by the research team is used for participation, which assigns random numerical TAN codes to each student to ensure pseudonymised data assessment. As the participants are minors, written consent is obtained from all students and their parents or legal guardians. The data collected is used exclusively for scientific purposes, is stored in secure databases and may be shared with other working groups for research purposes. Commercial use or sale of the data is prohibited.

The results on the effectiveness of the intervention will be published in international, peer-reviewed journals and presented at scientific conferences. In addition, participating schools will receive feedback in the form of reports, and the results will be published on public education platforms (e.g. Gateway), in school journals and shared with relevant stakeholders (educational institutions, teacher training centres, policy makers). The results will also be made available to the European Union as the funding institution (KA220-MV-22–36-89514).

Significant changes to the study protocol will be communicated immediately to the researchers involved, study participants, study registries and relevant journals.

Discussion

The SEL4@ll program offers an innovative approach to promoting social and emotional competencies, well-being and inclusion among European adolescents by combining a serious game with evidence-based principles of SEE and pedagogical material for teachers. This trial responds to the increasing need for scalable, engaging and inclusive interventions that address the social and emotional challenges faced by children and adolescents in a complex and digitalised world.

The advantages of using digital technologies in SEE in terms of engagement, accessibility and scalability outweigh the concerns about the growing digitisation of educational tools. Serious games can immerse students in realistic social situations and provide immediate feedback in a safe, playful environment, which can improve learning transfer and emotional engagement [48, 52]. Furthermore, digital delivery facilitates the standardisation of the intervention, reduces teachers’ workload and supports implementation in diverse educational environments.

The SEL4@ll programme is characterised by its school-wide, intercultural approach based on mixed methods. Collaboration with schools from four European countries (Germany, Italy, Spain and Finland) enables intercultural validation of the intervention and contributes to understanding how social-emotional learning (SEL) programmes can be effectively adapted to different educational and cultural contexts. The study uses a mixed-method approach, combining quantitative and qualitative methods. This enables a comprehensive evaluation of both the results and the implementation processes and provides insights into the mechanisms underlying successful implementation by considering the experiences of students and teachers.

However, some limitations must be considered. As with many digital interventions, potential risks include maintaining student engagement and preventing superficial use. Differences in school infrastructure, digital literacy, and teacher preparedness across countries may also influence fidelity of implementation. Furthermore, generalisability may be limited by the quasi-experimental nature of class-level randomisation and possible cluster effects, even though the study uses a randomised controlled design. Finally, although self-report measures are widely validated, they may be susceptible to social desirability and response bias.

Despite these challenges, the SEL4@ll program has the potential to make a significant contribution to the field of educational psychology and the well-being of adolescents. It advances the current state of research by combining theory-driven SEE principles with digital pedagogy, pursuing a cross-national design, and prioritising inclusivity and participatory development. If SEL4@ll proves effective, it could serve as a scalable model for embedding social-emotional learning in European education systems and digital learning environments.

Conclusions

The SEL4@ll project is an ambitious initiative to promote the social-emotional development of young people through an inclusive, evidence-based and digitally supported programme. By integrating a serious game into the framework of social and emotional education, the study aims to strengthen skills that are essential for personal development, well-being at school and social inclusion.

Through its rigorous mixed methods and intercultural design, SEL4@ll aims to provide valuable insights into the mechanisms, effectiveness and contextual adaptability of digital SEL interventions in European schools. Beyond its empirical contributions, the project is aligned with the European Union’s general educational and policy priorities and promotes equity, digital literacy and psychosocial well-being.

If successful, SEL4@ll could provide a replicable framework for promoting emotional competence, resilience and empathy among students, contributing to healthier, more inclusive and sustainable school communities.

Authors’ contributions

KS and FH drafted and wrote the protocol manuscript. KS, AM, AS, SP-Z collaborated in the development of the game narrative and psychological content. J-AL-Q, DNO, AAR contributed to the game development, graphic design and led the technical development of the serious game, including programming and gameplay optimisation. KS and FH secured funding for the study and obtained ethical approval. KS, FH, AM, AS, SP-Z participated in variable selection, supervised the overall study design and critically reviewed the manuscript. All authors read and approved the final manuscript.

Funding

This research was supported by the grant 2022-1-DE03-KA220-SCH-000089514, funded by the European Union’s Erasmus + Programme (KA220-SCH - Cooperation partnerships in school education). The funding institution had no role in study design, data collection, analysis, interpretation of data or the decision to submit the work for publication.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

Ethical approval has been granted by the University of Greifswald (BB 127/24a) and the University of Valencia (2024-PSILOG-3715935). The study will be conducted in accordance with the principles outlined in the Declaration of Helsinki. Parents/legal representatives of eligible children and adolescents will be asked to provide written informed consent; children and adolescents will be asked to provide their consent.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.