Universal design for learning for educating students with intellectual disabilities: a systematic review

Abstract

This review analyzes studies carried out between 2008 and 2018 which examined the educational impact of interventions based on the Universal Design for Learning (UDL) for students with Intellectual Disabilities (ID). The review aims to determine the research designs and methods of these studies, and their interventions and effectiveness. Seven studies met the inclusion criteria used in this review. The review demonstrated the diversity of research designs and methods used, which included quantitative, qualitative and mixed methods. The interventions included the use of digital environments, e-books, shared stories, audio systems, software and educational activities; all based on the principles of UDL. The reviewed studies confirmed the effectiveness of these interventions in educating such students, whether in academic, social or behavioral aspects. The study recommends further research to give greater clarification of the impact of UDL on the academic, social and behavioral aspects of the education of students with ID. It also recommends increasing the number of research participants and using a qualitative approach to better understand the lived experience of applying these interventions.

Introduction

Students with disabilities have faced a change in educational policies since the Education of All Handicapped Children Act (EHA) (1975), which focused on ensuring free and appropriate education according to individual needs. Then the Individuals with Disabilities Education Act (IDEA) (1997) gave them access to the General curriculum, but was amended in 2004 to conform to academic standards. More recently, Every Student Succeeds Act (ESSA) (2015) added a number of requirements. The most important of which was the use of Universal Design for Learning (UDL) in assessment and educational procedures to support students’ access to the general method. This law also it has suggested the use of technology to support education in line with the principles of UDL (Scott et al., 2017). Thus, UDL has become one of the most important programs supporting the inclusion of students with disabilities in general education. Among the most important categories of disability benefiting from previous laws are students with intellectual disability (ID) that is defined by the American Association for Intellectual and Developmental Disabilities (AAIDD) (2021) as ‘Intellectual disability is a disability characterized by significant limitations in both intellectual functioning and in adaptive behavior, which covers many everyday social and practical skills. This disability originates before the age of 22’ (Schalock et al, 2021).

The origin of UDL arose from the concept of Universal Design in architecture (UD), which focuses on designing buildings and roads in a way that allows the access of all beneficiaries, including those with disabilities. It is based on the principles of flexibility in use, fair and simple use, as well as the use of sensory information and simple physical effort (Jackson, 2005). According to this concept, UDL appeared to mean the framework or approach that enhances the access, participation and progress of all students in the general curriculum, including those with disabilities (Schreffler et al., 2019).

This framework was introduced in the 1990s in the United States of America by the Center for Applied Special Technology (CAST). CAST has become a pioneering body in adopting the principles of universal access to education, through the UDL (Schreffler et al., 2019). UDL can be defined as an educational planning and guidance framework that aims to increase beneficial access and reduce barriers to learning for students with special educational needs (CAST, 2011). It is a framework in which educational researchers, policy makers and practitioners meet the needs of an increasing number of diverse students while nevertheless acknowledging that there will always be students who need individualization when using assistive educational and technology techniques and method adjustments (Israel et al., 2014).

The UDL framework builds on modern neuroscience research, contemporary learning theories, and have benefited from digital technology flexibility. To make education more responsive to the diversity of learners, and removing barriers to them. Neuroscience suggests that human minds may look similar but are in fact as different and highly differentiated as fingerprints, as emphasized by anatomy, chemistry, and physiology. The brain is a complex and interconnected network, and learning takes place through a change in communication within and between those networks. UDL is based on three main networks: the affective networks responsible for motivation and participation, and the recognition networks that contribute to the perception of information in the surrounding environment and its transformation into knowledge. And strategic networks that plan and organize procedures and skills. This corresponds to the assumptions of education theorists as Vygotsky and Bloom who have established three fields of learning: emotional, cognitive, and skills (Meyer et al., 2014).

In addition to that, UDL project offers a customizable framework to inform the design of educational programs that cater to the potentially diverse needs of individual learners. This framework is informed by three core principles, which seek to ensure that educational courses foster engagement among students, use a variety of ways to represent learned information, and offer different ways to express and practice acquired knowledge (CAST, 2018). More specifically, engagement refers to strategies for increasing student motivation through the provision of meaningful choice in a non-threatening environment, enabling self-regulation, and enabling a range of feedback including self-assessment and mastery-oriented feedback. Representation refers to the provision of choices regarding the presentation of visual and auditory information to ensure that students are all equally capable of interacting with a particular learned topic. This can involve the use of multiple media, different languages, and pedagogic approaches focused on taking the time to check understanding and clarity of messaging. The final principle, namely the importance of action and expression, is based on the notion that learners should be given alternative ways to acquire and practice knowledge and skills. Alternative devices, control schemes, media and teaching approaches can be used to accommodate the needs of individual students, such as for different text speed or for different strategies to be viable in the completion of tasks. These principles combine to provide an outline for instruction and course design considerations like goals, methods, materials or assessments, in order to develop integrated, flexible approaches that are sensitive to the needs of each student (Burgstahler, 2001). Figure 1 shows the principles, guidelines, and checkpoints.

Figure 1.

The three principles of UDL.

Figure 1 © 2018 by CAST. All rights reserved. www.cast.org, www.udlcenter.org

UNICEF (2013) globally indicated that teachers are not ready to include students with disabilities, even if they are included in the classroom, so it is necessary to prepare teachers who are able to teach a variety of students, and the best way to do this is to train them on the best frameworks and practices that It has proven effective in teaching students with disabilities in inclusive classes, including UDL, thus demonstrating the importance of translating its principles and spreading them globally to support inclusion practices. The UDL framework has started spreading around the world through countries such as Canada, Australia, South Korea and Portugal. In addition, its principles and guidelines have been translated, on the website of the CAST Institute, into several languages, Such as Arabic, Chinese and others.

Policymakers and researchers suggest using UDL as a framework with flexible pathways to extend the inclusion of students with ID in public education, as they are usually taught in isolated environments, may only be integrated during activity and lunch times, or may be excluded from teaching times and educational experiences (Rao et al., 2017). What distinguishes UDL is that it does not require teachers to make adaptations in their teaching strategies to fit the needs of students with ID and others, but rather depends on proactive changes in the method at the basic level (Al Hazmi and Ahmad, 2018).

UDL has also been applied to the educational activities of students with ID in order to examine a variety of interventions (e.g. modified stories, educational aids) the results of which may appear in students’ interactions, perceptions, knowledge and behavior (Rao et al., 2017). In view of the importance of applying UDL in the education of students with ID, in 2015 the American Goals Committee for the American Association of Intellectual and Developmental Disabilities (AAIDD) set two specific goals for UDL to develop educational services that support the needs of students with intellectual and developmental disabilities (Thoma et al., 2015). The first objective is to evaluate the implementation and application of UDL within educational environments, including obstacles to implementation, and the roles of special and general education personnel in implementation. The second objective is to research the effectiveness of UDL as a universal framework for teaching methods and assessment in its broad application within the basic education stage (Lowrey and Smith, 2018).

Despite the importance of UDL, the impact of its interventions has been studied in only a few countries with samples from very similar cultural, social and economic backgrounds. Also, most experimental studies have been conducted in North America, with rare exceptions in other regions, cultures and types of students (Al-Azawei et al., 2016, Mangiatordi and Serenelli, 2013). Accordingly, Rao et al. (2017) summarized the existing set of research studies on UDL for students with ID in schools. Their article was intended to identify the basic questions that could guide future research into UDL. By reviewing all available studies, they concluded that there was a need to define how the framework is applied in the method, how individual support is provided, and how UDL can be used in conjunction with evidence-based practices and multiple support systems in schools. This encouraged the carrying out of methodical reviews to identify existing experiences of applying this framework with students with ID. So this systematic review has moved towards more in-depth objectives, which is to determine the methods and interventions used in that research and how they are related to UDL and their effectiveness in teaching ID students.

According to this move towards studying educational practices based on UDL in the education of students with ID, this study came to focus on reviewing those research studies that dealt with UDL as a framework for the education of students with ID during the period 2008 − 2018. This was done by reviewing interventions and practices based on UDL, analyzing the research methods and designs that have been applied, and then evaluating the results and effectiveness of the interventions in terms of academic, behavioral and social aspects. Thus, this study may provide a summary for researchers and practitioners on how to design and implement effective UDL-based interventions and practices in teaching students with ID. Thus, this study seeks to answer the following questions regarding the identified studies:

1. What methods did the researchers use to study UDL-based interventions in teaching students with ID?

2. What types of UDL-based interventions were used to teach students with ID?

3. How effective were the UDL-based interventions in educating students with ID?

Method

The databases searched were Education Journals, ProQuest Web of Science, ERIC, Google Scholar, Education Research, and Complete EBSCO, in addition to manual research in the sources of previous studies. The search was conducted using the keywords Universal Design for Learning and intellectual disability, and their synonyms in English such as: UDL, Severe Disabilities, Primary, Developmental Disabilities, Mental Retardation, elementary and secondary.

The initial research resulted in the identification of (71) studies. They were revised and included as appropriate based on the following inclusion and exclusion criteria:

1. The study contains the UDL term in title or abstract;

2. All or some of the study participants have ID;

3. The study has an empirical basis, whether the data was collected in a quantitative or qualitative manner, as one case study or a mixed approach;

4. The study was published in the English language in a scientific journal;

5. The study was published between 2008 and 2018;

6. University theses and books are excluded;

7. Studies in post-secondary or pre-school levels are excluded.

Of the 71 studies reviewed, the largest number of studies was excluded because there was no UDL-based intervention. While 13 preliminary studies were identified that included an intervention or practice based on UDL, two of these were excluded in a second review because they were published in 2006, three because they applied at the undergraduate level, and one because it applied at the pre-school stage. This left seven studies to be reviewed in this article.

Results and discussion

Data extraction

The following information was extracted from the seven selected studies to address the study questions. It is summarized in the Table1 that includes six columns as follows: authors and year of publication, participant's information, method of study, tools used, type of UDL-based intervention in the study, and study results. The seven studies were coded to extract the required information using a coding sheet dedicated to this purpose. Where three articles were examined and coded as a team to ensure the researchers' agreement and to ensure mutual understanding of the required information. Then the work was distributed to the authors so that each researcher has two studies.

The information extracted from the seven studies and summarized in Table 1 can be used to answer the study questions, as follows:

Table 1.

Extracted studies.

Author's name and year	Sample number + location	Methodology	Tool	UDL-based interventions	Results
Browder et al. (2008)	3Students with intellectual and health disabilities were the most difficult to respond to reading and writing / language lessons, in the separate semester. School in the southeastern United States of America	Single-case design Multiple investigation by participants	Task analysis Notes	Plan and implement joint stories for three students with multiple disabilities using principles of UDL	-Student 1’s response improved by 97%, student 2’s by 94% and student 3’s by 92%. - UDL increased commitment to reading and writing and enhanced children's communication skills. The study provided an important strategy to ensure students fully participated in the lesson.
Coyne et al. (2017)	10 students and 7 teachers (4 lead teachers and 3 assistants). The study was conducted at a public special education school in a northeastern suburb of the United States serving primary and middle school students.	Qualitative study - the rooted theory	(A) Weekly class notes (B) Student and teacher interviews (C) Check the electronic usage record data (D) Online student comments and projects	Used Udio, a digital literacy learning environment based on UDL principles, used to support literacy education activities for middle school students with intellectual and developmental disabilities	-Students were able to interact with the UDL environment that provided socially original interactions with their peers of the same age. -Individual choice and independence were improved and appropriate levels of challenge and support were provided. -Students with ID could actually benefit from educational practices that were previously thought to benefit only general education students.
Coyne et al. (2012)	9 teachers of students with significant ID, whether in universal or semi-separate classes. 16 students with significant ID were selected from grades k-2.	Semi-experimental	Reading growth was assessed using Woodcock- Johnson Tests - third edition	UDL-based reading education approach, Literacy by Design (LBD), combining UDL e-books and letter and word recognition software	-The LBD group achieved, on average, significantly higher outcomes in comprehension than the control group, indicating a strong intervention effect. Impact size analysis indicates that the LBD's influence was also strong on students’ skills in word recognition, auditory comprehension, and concepts about printing.
Kennedy et al. (2014)	141 high school students participated in two groups: 32 with disabilities (including 2 with ID), 109 without disabilities.	Semi-experimental	Wechsler Individual Achievement Test (WIAT-II) СВМ Methodological Assessment	A multimedia-based educational tool called Content Acquisition (Podcasts) (CAPs) which are multimedia-based educational modules with presentations and sounds built in a manner consistent with: (a) UDL principles for multimedia representation and participation (CAST, 2011), and (b) Mayer's Knowledge Theory and Multimedia Learning. The CAPs procedures are based on carefully selected, evidence-based educational tools appropriate for educational content.	- The average score for the CAP group (students with disabilities) on CBM was significantly higher than the other group in both modules and in the final test. - During the eighth week of education, CBM grades tended to become more variable, which meant students were learning at faster rates. - The results of this study show that when using CAPs based on the principles of UDL and evidence-based instructional methods, students with disabilities learn vocabulary and content at a faster rate and in a more robust way than when taught using the regular method.
Kortering et al. (2008)	290 students, including 37 with severe acute disabilities, 17 (6%) identified as having specific learning disabilities, 6 (2%) as disordered behavior, and 2 as moderate ID.	Mixed methods	Self-participation scale of students. It evaluated students' perceptions of their participation when making UDL interventions. Some questions were closed and three were open-ended.	24 interventions (14 in algebra and 10 in biology); 14 technologies used; 10 relied on the same activity as a key to incorporating the UDL concept.	Algebra and biology participants demonstrated strong levels of positive alignment with efficacy, benefit, and satisfaction with UDL interventions, as opposed to the other academic groups. Both groups consistently reported favorable assessments regarding learning important and useful information, and information to help them take their exams, stay on the task and work. The authors’ experience suggested that UDL may be the best way to improve current teacher practices to allow more students to engage in learning and enjoy high school
Loman et al. (2018)	3 students in separate urban public elementary schools, from kindergarten through grade five in the Northwest Pacific region, that were implementing the Schoolwide Positive Behavioral Interventions and Supports (SWPBIS) program.	Single-case design Multiple baselines	Following the duration of student problem behavior using a stopwatch or digital timer	SWPBIS standard lessons at each participating school based on UDL principles to make it accessible to students with severe disabilities for use in comprehensive school settings (e.g. cafeteria, corridors).	The duration of the problem behavior for Craig showed an immediate change in level and direction, and it decreased steadily to an average duration of 17.2 s. The intervention improved accessibility to the system (SWPBIS) in the interlaced school settings, and led to a decrease in the problem behavior of the participants. Each participant showed an immediate change in the level of duration of the problem behavior from baseline to the end of the intervention that taught students routine and special expectations in school settings (such as cafeteria, entrance and class line). Students were able to express mastery of content by practicing behaviors rather than simply repeating expectations.
Scott et al. (2011)	6 students at secondary level (5 with ID and 1 with learning disabilities); independent high school semester for academic education for social studies in the southeast of USA.	Multi-ABAC design Single-case design	To measure achievement (scores of working papers) (computer-based assessment) Participation scale	Two interventions were used. (1) reflected the UDL method, to teach and evaluate students involved in learning through audiovisual and practical activities; technology was integrated in lesson planning and presentation with audio and video to enhance the representation of educational information. (2) the first intervention was used in conjunction with multiple transitional aspects and the information taught related to the skills of the adult world.	The combination of the UDL approach and the elements of effective transitional education for teaching academic content improved student participation and interest in lessons and ultimately in student academic achievement. We found that students demonstrated greater interest and participation in lessons designed and presented using the UDL approach and even more interest and participation in Universal design for transition (UDT) lessons.

The first study question

What research designs and methods did researchers use to study UDL-based interventions in teaching students with ID?

The table summarizes the descriptive features of the seven studies that were reviewed. Regarding the overall sample of the seven studies, the total number of students with ID participating in all studies was 41. From five of the studies there were 15 females and 22 males; two of the studies did not specify the gender, so four students were of unspecified gender.

Four of the studies included other disabilities besides ID, learning disabilities, autism and behavioral disorders (Kennedy et al., 2014, Kortering et al., 2008, Loman et al., 2018, Scott et al., 2011), while the other three focused on students with ID only (Browder et al., 2008, Coyne et al., 2017, Coyne et al., 2012). The level of intellectual disability in studies ranged from mild to severe. Intervention procedures were conducted in separate special classes in three of the studies (Browder et al., 2008, Coyne, et al., 2017, Loman et al., 2018) whereas, in the other four studies, interventions were conducted in inclusive classrooms (Coyne et al., 2012 Kennedy et al., 2014, Kortering et al., 2008, Scott et al., 2011). Four of the studies were conducted at the primary or intermediate stage (Browder et al., 2008 Loman et al., 2018, Coyne et al., 2017, Coyne et al.,2012) and the other three at the secondary stage (Kennedy et al., 2014, Kortering et al., 2008, Scott et.al., 2011). Thus, all the reviewed studies gave an accurate description of the context in which the study was conducted, with demographic information being provided about the sample. This is very important in order to allow other researchers to repeat studies accurately, as confirmed by Rao et al. (2014).

As for the research designs, these varied between quantitative, qualitative and mixed according to the following distribution: two were semi-experimental (Kennedy et al., 2014, Coyne et al., 2012); three were one-state designs, which included reverse and multiple designs (Browder et al., 2008, Loman et al., 2018, Scott et al., 2011); one was a qualitative study following the methodology of rooted theory (Coyne et al., 2017), and one was a mixed methods study (Kortering et al., 2008).

In all designs the results were positive and the interventions effective. To measure their impact, the researchers used a variety of measurement tools that included interviews, observations, record reviews and opinion polls, as well as standardized tests such as Woodcock-Johnson and Wechsler Individual Achievement Test (WIAT-II). Method-based assessment, computer-based assessment and worksheets were used.

The second study question:

What types of UDL-based interventions were used to teach students with ID?

It can be seen from the table that the researchers applied the principles of UDL in a variety of ways and through different types of intervention. The interventions included digital environments on the Internet which incorporated educational methods, activities and techniques built according to the principles of UDL. They also included the use of software, e-books, shared stories, videos and classroom management systems that fulfilled UDL principles. They applied both individual and group teaching. The reviewed studies gave detailed descriptions of how these interventions incorporated the three UDL principles.

All of the studies except Loman’s examined the application of these interventions at the semester level. Also, all the studies apart from Loman’s targeted academic achievement, but Loman’s focused on the behavioral aspect of students with ID at the school level.

Looking at the key practices reported by each study individually, in Browder’s study three joint story books were chosen to teach reading and writing, then each story was adapted according to the principles of UDL and according to the student's need; to create added interest, the main character in the story was given the student’s name.

Coyne et al. (2017) used Udio, a UDL-based digital literacy learning environment which aims to improve understanding of reading and foster interest in reading by students deprived of traditional practices. Udio combines research on motivation to read with evidence-based literacy practices. It provides students with sustainable and rigorous learning opportunities through access to highly beneficial content, choosing reading materials based on student’s interest, and engaging in social experiences with text and access to reading and writing support.

In Coyne et al. (2012)’s study the intervention included four universally designed digital story books. The primary focus of these e-books was comprehension, phonemic awareness, phonics education, vocabulary, and fluency with a set of exercises and interactive games. The embedded supports are based on the three principles of UDL. In addition to e-books, students used two complementary programs. The combination of e-books, e-book library and letter and word play program provided access to a wide range of materials that support the teaching of the five core areas of reading.

The intervention in Kennedy et al. (2014)’s study focused on teaching and acquiring the vocabulary of social studies course content and improving student performance, by designing an educational tool with multimedia presentations and voices based on UDL principles and evidence-based practices. Kortering et al. (2008)’s study incorporated 14 assistive technology and 10 educational activities, all based on UDL principles, in teaching algebra and biology.

In the study by Loman et al. (2018), typical school SWPBIS lessons were reinforced in ways based on UDL principles to make them accessible to students with severe disabilities in comprehensive school settings, e.g. in cafeterias and corridors. Lessons included printed words and phonemic and oral interpretations, allowing students to express their knowledge of behavioral expectations through speaking, acting or other means; social stories were also used.

Scott et al. (2011) used two interventions to teach students at the secondary level. The first was developed to reflect the UDL method of teaching and evaluating students who were learning through audiovisual and practical activities, where technology was incorporated into lesson planning and presentations were enhanced with audio and video. The second intervention led on from the first and was used in conjunction with multiple transitional areas and the information taught was related to the skills of the adult world.

Previous diversity of interventions, content, and classroom practices is due to the nature of the UDL as a framework that includes guidelines that are in the form of a list of options that give flexible instructions and provide proactive support for any practice. Therefore, researchers who strive to demonstrate the effectiveness of UDL-based interventions are keen to accurately describe and link their interventions with UDL principles and guidelines as in Figure 1, which facilitates the replication and development of studies (Rao et al., 2017).

The third study question:

How effective were UDL-based interventions in educating students with ID?

To answer this question, the results of the studies were included in the last column of the table, which shows the impact of the interventions in the studies reviewed. All the studies reported positive results, indicating the significance of the UDL approach for the education of students with ID except for one study (Loman et al., 2018) focused on the behavioral aspect of students with ID.

It is noted in the studies that used the one-case design (Browder et al., 2008, Scott et al., 2011) that the effect on academic achievement was high and effective for the UDL method as all participating students improved in terms of reading and writing levels, level of interest, and active participation in lessons. Improvement rates reached 97%.

As for the semi-experimental studies, Coyne et al. (2012)’s indicated that the experimental group with ID achieved significantly more highly in reading comprehension, fluency, auditory awareness and vocabulary compared to traditional teaching, which indicates a strong influence of the intervention. The other one, by Kennedy et al. (2014), did not specify the outcome for students with ID separately but gave results in general for the range of participating students, including those with ID. The results indicate a significant academic improvement in vocabulary learning and content acquisition compared to traditional teaching.

Looking at the mixed methods study, by Kortering et al. (2008), its results confirmed that the participants feel satisfied and comfortable during the algebra and biology lessons, that the information was important and useful them, and that the intervention helped them to stay on task.

A study by Coyne and co-workers, which used a qualitative method, gave both academic and social results, as the use of UDL-Based Digital Environments provided social interaction for students with ID with their peers. The results showed improvement of individual choice and independence and the emergence of a high level of challenge and support. In addition, students were able to benefit from the academic content and practices that were formerly believed only to be suitable for students in general education.

The results of Loman et al. (2018)’s single case study differed from those of the other six studies as it focused on the behavioral aspect. It investigated the effect of supporting positive behavioral interventions at the school level with the three UDL principles on three students with severe disabilities. The focus here was on the result for the single student (Craig) with intellectual disability. The results showed that the intervention led to an immediate change in the level and direction of the student's bad behavior (screaming, beating others). The level of change from the baseline to the intervention stage was very large, with an improvement of 90%, which improved the child's access to the school system so he was then able to succeed in the daily routine.

The results of the studies generally showed that teaching students with ID based on UDL principles was useful in acquiring diverse academic content including literacy, algebra, science and social studies. The results also included social and behavioral aspects such as independence, peer interaction, survival on the job, and reduced inappropriate behavior. In addition, all studies recommended further research to verify the impact of UDL on academic, social and behavioral aspects. The results also emphasized the need to increase the number of participants in such research and to use a qualitative approach to gain a better understanding of the reality of the application of these interventions.

Implications for practice

The results of this review indicate that the UDL-based interventions were beneficial to students in general, and the results of the studies reviewed showed that teaching students with IDbased on UDL principles was beneficial in acquiring a variety of academic content including: teaching reading and writing, algebra, science, Social Studies. The UDL-based interventions provided flexibility and scaffolding that support access to general education curricula for students with ID, and the results of the studies included the development of social and behavioral aspects such as: independence skills, interaction with peers, staying on task, and a decrease in bad behaviors.

Limitations

The results of this review were based on only 7 studies that were consistent with the criteria of this review, as it is evident from the dates of these studies that they were confined to the years 2008–2018 only. Furthermore, we found that UDL implementation and the accuracy of the research designs varied in these seven studies. Thus, it is difficult to know which UDL principles reliably predictable effect magnitude in UDL-based intervention studies. Whereas, a consistent reporting measure has not been used for quantitative studies.

Recommendations and future research directions

We recommend that future research be conducted to verify the effectiveness and impact of UDL interventions on the academic, social, and behavioral aspects of students with ID, using experimental research methods, either for groups or single-case designs. More rigorous research designs and procedures should be used to demonstrate the functional relationship between UDL-based interventions and dependent variables. We also recommend that UDL principles and guidelines be used more explicitly, and that these principles be closely linked with the interventions used. Another recommendation for future studies is to increase the conduct of qualitative research to better understand the nature of those UDL-based interventions and the behavior and needs of students with IDand their teachers in the classroom.

Conclusion

In conclusion, the UDL-based interventions in teaching students with ID that were included in this review of seven studies included the use of digital environments, e-books, shared stories, audio systems, software, and educational activities. They were shown to be effective in teaching academic, social and behavioral aspects to students with ID. The reviewed studies indicated that more research is still needed to verify the effectiveness and impact of UDL interventions, by increasing the number of participants in experimental research, and by using a broader qualitative method to improve understanding of the context of implementing these interventions.

Disclosure statement

No potential conflict of interest was reported by the authors.