The proposed site-level randomized trial will test the effectiveness of a work site intervention based on an ecological framework at preventing weight gain among high school employees in Massachusetts. The investigators hypothesis is that the intervention will positively impact healthy dietary patterns and physical activity, perceived organizational commitment, coworker influences, social support, self-efficacy, and self-control, which in turn will positively mediate or moderate the positive associations between the intervention and the primary outcomes (change in weight, BMI, and waist circumference). If effective, the intervention is designed to be generalizable to high school settings across the country and has the potential to reduce the morbidity, mortality and economic costs of overweight and obesity in this important population.