This article provides a systematic review and meta-analysis of the current evidence for universal school-based (USB) social and emotional learning (SEL) interventions for students in kindergarten through 12th grade available from 2008 through 2020. The sample includes 424 studies from 53 countries, reflecting 252 discrete USB SEL interventions, involving 575,361 students. Results endorsed that, compared to control conditions, students who participate in USB SEL interventions experienced significantly improved skills, attitudes, behaviors, school climate and safety, peer relationships, school functioning, and academic achievement. Significant heterogeneity in USB SEL content, intervention features, context, and implementation quality moderated student experiences and outcomes. Strengths and limitations of this evidence and implications for future USB SEL research, policy, and practice are discussed.