While overall prevalence of obesity improved in Massachusetts public schools between 2009 and 2014, prevalence remained unchanged for children living in poor, rural, and smaller communities. This project will identify which programs and activities have been effective in reducing childhood obesity among the successful schools, and use the information to guide future interventions for those schools that were not. Specific aims of this study are to: 1) investigate the roles of school policies, healthy eating and physical education programs, and community social and built environments in the decline in obesity prevalence among Massachusetts public school students; 2) identify necessary and sufficient conditions for significantly reducing obesity prevalence in public schools; and 3) recommend approaches to accelerate the decline and reduce socioeconomic and geographic disparities in obesity prevalence in public schools. The research team will use a mixed methods approach to identify both necessary and sufficient school and community conditions for reducing obesity prevalence in public schools using a retro- and prospective cohort design. Researchers will analyze over 2.1 million body mass index (BMI) records from 338 school districts for public school students grades 1, 4, 7, and 10 between 2009 and 2017 and correlate them with school-level administrative data on healthy eating and physical education programs and community social and built environmental data from the same period. Analytic reports and district-specific recommendations will be shared with the Massachusetts Departments of Public Health and Elementary and Secondary Education and all Massachusetts public schools.