Background: The school environment plays a key role in adolescents’ emotional development and well-being, yet little research has compared self-harm and related psychosocial problems across different secondary school types.

Methods: Using data from the Growing Up in Ireland (GUI) longitudinal cohort, this study examined differences in the prevalence of self-harm and psychosocial risk factors across different school types: single-sex versus coeducational, fee-paying versus non-fee-paying, disadvantaged versus non-disadvantaged, and schools with different religious ethos. Multilevel regression models distinguished school-level from individual-level effects.

Results: Almost all variance in self-harm and most of the variance in psychosocial problems associated with self-harm occurred at the individual level. Higher self-harm prevalence in single-sex girls’ schools was accounted for by the greater concentration of girls, who had over twice the odds of self-harm compared with boys (OR 2.1, 95% CI 1.71–2.69). No significant differences in self-harm were found by school socio-economic status or religious ethos. Disadvantaged schools showed higher prevalence in seven of nine psychosocial problems, although only internalising problems and truancy/absenteeism remained significantly associated with disadvantaged schools in the fully adjusted models. Adolescents whose parents reported having a religion were less likely to self-harm (OR 0.62, 95% CI 0.50–0.75).

Discussion: Although schools are important settings for self-harm prevention, findings indicate that interventions should primarily target individuals and high-risk groups. Girls, in particular, may benefit from supports addressing self-harm. Disadvantaged schools, where well-established psychosocial risk factors for self-harm are more common, may benefit from well-being programmes targeting internalising problems and truancy/absenteeism.