This is a group-randomized trial involving 20 elementary schools in Jefferson Parish public schools. Schools will be the unit of randomization; 10 schools will be randomly allocated to implement the intervention, and 10 schools will serve as controls. The primary aim of the program is to reduce mean body weight. Secondary aims relate to changes at both the individual level and the environmental level. The intervention will address the two major determinants of overweight and obesity: physical activity and diet. A School Wellness Committee at each site will be instrumental in identifying and implementing components of the intervention.