Conventional systematic reviews offer few insights into for whom and how interventions work. 'Realist reviews' examine such questions via examining 'context-mechanism-outcome configurations' (CMOCs) but are insufficiently rigorous in how evidence is identified, assessed and synthesised. We developed 'realist systematic reviews', addressing similar questions to realist reviews but using rigorous methods. We applied this to synthesising evidence on school-based prevention of dating and relationship violence (DRV) and gender-based violence (GBV). This paper reflects on overall methods and findings, drawing on papers reporting each analysis. Drawing on intervention descriptions, theories of change and process evaluations, we developed initial CMOC hypotheses: interventions triggering 'school-transformation' mechanisms (preventing violence by changing school environments) will achieve larger effects than those triggering 'basic-safety' (stopping violence by emphasising its unacceptability) or 'positive-development' (developing students' broader skills and relationships) mechanisms; however, school transformation would only work in schools with high organisational capacity. We used various innovative analyses, some of which aimed to test these hypotheses and some of which were inductive, drawing on available findings to augment and refine the CMOCs. Overall, interventions were effective in reducing long-term DRV but not GBV or short-term DRV. DRV prevention occurred most effectively via the 'basic-safety' mechanism. 'School-transformation' mechanisms were more effective in preventing GBV but only in high-income countries. Impacts on long-term DRV victimisation were greater when working with a critical mass of participating girls. Impacts on long-term DRV perpetration were greater for boys. Interventions were more effective when focusing on skills, attitudes and relationships, or lacking parental involvement or victim stories. Our method provided novel insights and should be useful to policy-makers seeking the best interventions for their contexts and the most information to inform implementation.