Participants
Participants were school-students, aged 13–15 years old. Students in classes where the majority were 14 years old were invited to participate (n = 1602) and 69% (n = 1112) completed a baseline self-report questionnaires. Follow-up questionnaires were administered at 3-months and 12-months after baseline, with 89% (n = 993) and 86% (n = 959) taking part at 3-months and 12-months, respectively (Fig. 
CONSORT diagram of the Irish site of the SEYLE study. (Note: Grey shading indicates the intervention period. Partial PEs data indicates the number of individuals who provided at least one wave of PEs data. These individuals were included in the main analysis. A supplementary analysis restricted to participants who provided data at all three waves of the study is presented in eAnalysis 1)