Diab 2015.

Study characteristics
Methods	Study design: cluster‐RCT Study grouping: parallel group Cluster size: 30 children (mean) Study duration: 24 weeks
Participants	Inclusion criteria: children aged 10–13 years; selection from 2 regions (North Gaza and Gaza City); random sampling of 2 schools in both areas from a numbered list of schools; within each of the 4 schools, 2 boys' and 2 girls' classes were randomly sampled by using a lottery tool. Exclusion criteria: not reported Age range: 10–13 years Gender: 50.6% boys, 49.4% girls Intervention sample: 242 Control sample: 240 Main type of traumatic event: bereavement Phase of humanitarian crisis: after the acute crisis (mortality was similar or less than what it was before the crisis). 3.5 months after the War on Gaza ended Type of humanitarian crisis: protracted emergencies, war/armed conflict
Interventions	Intervention name: Teaching Recovery Techniques (TRT) Delivered by: professionals: 2 female and 2 male counsellors (master's degree in psychology and training in counselling, including the TRT techniques) Format of therapy: face to face Number of sessions (total): unclear Type of control: waiting list Type of intervention context: group sessions in school setting Type of promotion intervention: group level Description of the intervention: the TRT is a manualised intervention for traumatised children to learn how to cope effectively with the symptoms of post‐traumatic stress. For example, relaxation exercises and sleep hygiene are expected to attune hyperarousal symptoms, manipulation of mental imagery to gain control of intrusive symptoms, and graded exposure techniques are trained to deal with avoidance symptoms. The TRT involved symbolic elements of play, drawing, writing, and narrating, as well as psychoeducation about normal and worrying trauma responses.
Outcomes	The cluster effects were controlled for all the classes. Mental well‐being Outcome type: continuous outcome Reporting: fully reported Scale: Mental Health Continuum–Short Form (MHC–SF) Direction: higher is better Data value: endpoint Prosocial behaviour Outcome type: continuous outcome Reporting: fully reported Scale: SDQ Direction: higher is better Data value: endpoint Acceptability (dropout from trial) Outcome type: dichotomous outcome Reporting: fully reported Data value: endpoint
Notes	Sponsorship source: Academy of Finland (grant #215555) Country: Palestine Setting: school classes in Gaza Author's name: Marwan Diab Institution: University of Tampere, Finland Email: diabmarwan@gmail.com Address: School of Social Sciences and Humanities/Psychology, FIM‐33014 University of Tampere, Kalevankatu 5, Linna 4krs, Finland
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The sample consisted of 482 children whose ages were 10–13 years (M [mean] = 11.29, SD = .68; 50.6% were boys) and who were randomly selected either to the intervention (n = 242) or to the control‐waiting list group (n = 240)." No further information reported on the method of random sequence generation, but the balance of participant level characteristics suggests that the randomisation procedures were successful.
Allocation concealment (selection bias)	Unclear risk	Allocation concealment procedures were not reported.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Blinding procedures were not reported; however, it is likely that participants were aware of their intervention allocation as the trial was open‐label.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No information provided.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "There were no drop‐outs between T1 and T2 because children were assessed in their schools during the same semester."
Selective reporting (reporting bias)	Unclear risk	All measures described in the methods section of the article were also reported in the results. No trial protocol/registration number available.
Therapist qualification	Low risk	Quote: "two female and two male counsellors (master's degree in psychology and training in counselling, including the TRT techniques)."
Therapist/investigator allegiance	Unclear risk	No information provided.
Intervention fidelity	Low risk	Quote: "The intervention fidelity was guaranteed by weekly supervision by the last author (SQ), including case studies, psychodrama of TRT tools, consultation sessions and practical guiding in the schools."
Other bias	Low risk	No other sources of bias can be detected. Cluster‐RCT risk of bias extension 1. Recruitment bias; the recruited population belonged to the same catchment area (low risk of bias) 2. Baseline imbalance; cluster balance was maintained after randomisation (low risk of bias) 3. Loss of clusters; none of the clusters were lost (low risk of bias) 4. Incorrect analysis; the analyses were correctly conducted and reported (low risk of bias)