CONTEXT: Previous reviews of mental health interventions have focused on adolescents (10-19 years), with a paucity of comprehensive evidence syntheses on preventive interventions for school-aged children (5-10 years). OBJECTIVE: To summarize and synthesize the available evidence from systematic reviews of mental health and positive development interventions for children aged 5-14.9 years in both high-income (HIC) and low- and middle-income countries (LMIC), with a focus on preventive and promotive strategies. DATA SOURCES: This overview includes all relevant reviews from OVID Medline, The Cochrane Library, and Campbell Systematic Reviews through December 2020. STUDY SELECTION: We included systematic reviews that synthesized empirical studies using experimental or quasi-experimental designs to evaluate the effectiveness of interventions in children aged 5-14.9 years. DATA EXTRACTION: Data extraction and quality assessment were completed independently and in duplicate by two review authors. The AMSTAR2 tool was used to assess methodological quality. RESULTS: We included 162 reviews. The greatest evidence was found in support of school-based universal and anti-bullying interventions in predominantly HIC. Moderate evidence was found for the use of substance abuse prevention, and early learning and positive development interventions in mixed settings. In LMIC-only contexts, the most promising evidence was found for positive youth development programs. LIMITATIONS: The review was primarily limited by paucity of high-quality research due to methodological issues and high heterogeneity. CONCLUSIONS: This overview of reviews highlights the need for further research to consolidate findings and understand the specific criteria involved in creating positive mental health and development outcomes from the various interventions considered.