This study uses natural and virtual experiments, including environment/policy and education/promotion interventions, to identify specific interventions effective in promoting walking and physical activity among elementary school children in Austin, TX who are at high risk of developing obesity. The level of relative risk will be determined based on race, income, gender, healthcare access, transportation mobility, and acculturation. Natural experiments involve school administrative boundary changes, school transfers, sidewalk improvements, and street-crossing safety improvements. Virtual experiments will assess potential and feasible changes in the street, playground, and park designs that may influence children’s and their parents/guardians’ activities during the day and night. This study identifies the barriers (why not active) and motivators (why active), and compares similarities and differences across different sub-groups of children. This study also ensures its policy relevance by consulting with local and state policy makers throughout the research process and by translating the findings into policy decision-support tools and policy recommendations.