The European Union Dataprev project reviewed work on mental health in four areas, parenting, schools, the workplace and older people. The schools workpackage carried out a systematic review of reviews of work on mental health in schools from which it identified evidence-based interventions and programmes and extracted the general principles from evidence-based work. A systematic search of the literature uncovered 52 systematic reviews and meta-analyses of mental health in schools. The interventions identified by the reviews had a wide range of beneficial effects on children, families and communities and on a range of mental health, social, emotional and educational outcomes. The effect sizes associated with most interventions were generally small to moderate in statistical terms, but large in terms of real-world impacts. The effects associated with interventions were variable and their effectiveness could not always be relied on. The characteristics of more effective interventions included: teaching skills, focusing on positive mental health; balancing universal and targeted approaches; starting early with the youngest children and continuing with older ones; operating for a lengthy period of time and embedding work within a multi-modal/whole-school approach which included such features as changes to the curriculum including teaching skills and linking with academic learning, improving school ethos, teacher education, liaison with parents, parenting education, community involvement and coordinated work with outside agencies. Interventions were only effective if they were completely and accurately implemented: this applied particularly to whole-school interventions which could be ineffective if not implemented with clarity, intensity and fidelity. The implications for policy and practice around mental health in schools are discussed, including the suggestion of some rebalancing of priorities and emphases.