BACKGROUND: Whole-school interventions go beyond classroom health education to modify the school environment to promote health. A sub-set aim to promote student commitment to school to reduce substance use and violence (outcomes associated with low commitment). It is unclear what factors influence implementation of such interventions. METHODS: We conducted a systematic review including synthesis of evidence from process evaluations examining what factors affect implementation. Meta-ethnographic synthesis was informed by May's General Theory of Implementation. RESULTS: Sixteen reports, covering 13 studies and 10 interventions were included in our synthesis. In terms of May's concept of 'sense-making', we found that school staff were more likely to understand what was required in implementing an intervention when provided with good-quality materials and support. Staff could sometimes wilfully or unintentionally misinterpret interventions. In terms of May's concept of 'cognitive participation', whereby staff commit to implementation, we found that lack of intervention adaptability could in particular undermine implementation of whole-school elements. Interventions providing local data were reported as helping build staff commitment. School leaders were more likely to commit to an intervention addressing an issue they already intended to tackle. Collaborative planning groups were reported as useful in ensuring staff 'collective action' (May's term for working together) to enact interventions. Collective action was also promoted by the presence of sufficient time, leadership and relationships. Implementation of whole-school interventions took time to build. Considering May's concept of 'reflexive monitoring' (formal or informal review of progress), this was important in assessing and enhancing implementation. 'Quick wins' could help maintain collective impetus to implement further intervention activities. CONCLUSION: We identified novel factors influencing implementation of whole-school elements such as: local adaptability of interventions; providing local data to build commitment; interventions addressing an issue already on school leaders' agenda; collaborative planning groups; and 'reflexive monitoring' as an explicit intervention component.