Background
LGBTQ+ young people have elevated rates of poor mental health in comparison to their cisgender heterosexual peers. School environment is a key risk factor and consistently associated with negative mental health outcomes for LGBTQ+ adolescents.

Aims
To examine how, why, for whom and in what context school-based interventions prevent or reduce mental health problems in LGBTQ+ adolescents.

Methods
A realist review methodology was utilised and focused on all types of school-based interventions and study designs. A Youth Advisory Group were part of the research team. Multiple search strategies were used to locate relevant evidence. Studies were subject to inclusion criteria and quality appraisal, and included studies were synthesised to produce a programme theory. Seventeen studies were included in the review.

Results
Eight intervention components were necessary to address LGBTQ+ pupils mental health: affirmative visual displays; external signposting to LGBTQ+ support; stand-alone input; school-based LGBTQ support groups; curriculum-based delivery; staff training; inclusion policies; trusted adult. Few school-based interventions for this population group were identified.

Conclusions
The programme theory indicates that “to work” school-based interventions must have a “whole-school” approach that addresses specifically the dominant cis-heteronormative school environment and hence the marginalisation, silence, and victimisation that LGBTQ+ pupils can experience.