Our long-term objective is to reduce the rates and risk of childhood obesity via school-based nutrition and physical activity policies. Using a randomized design, we propose to monitor and evaluate how Connecticut's first-ranked District Wellness Policy, in the New Haven Public School district, is implemented and determine its impact on children's obesogenic behaviors, weight outcomes, and school performance. This study is designed to significantly advance empirical research on school wellness policies and to provide important evidence to guide future interventions in schools and communities - translating science to improved health of the public.