The overall goal of this project is to assess when, where and to what extent school playground environmental interventions increase children's physical activity, and to use these results to inform local advocacy efforts to prevent obesity in low-income and minority children.  The target population is fourth-grade children and their parents (50% of whom will be from low-income families) from four mid-Missouri elementary schools.  Researchers will use geographically tagged physical activity (accelerometer) data to evaluate children's response to an environmental intervention and investigate children's perspectives (as well as those of their parents) regarding the participatory process used to design the intervention and why children may have responded to it as they did.  Children in the study will be involved in the dissemination activities so that their voice is heard by decision-makers who will develop further environmental interventions or policies to benefit them.