Recess periods often lack the structure needed to support physical activity and positive social development (Robert Wood Johnson Foundation 2010). The Playworks program places full-time coaches in low-income schools to provide opportunities for organized play during recess and throughout the school day. Playworks activities are designed to engage students in physical activity, foster social skills related to cooperation and conflict resolution, improve students' ability to focus on class work, decrease behavioral problems and improve school climate. The Robert Wood Johnson Foundation (RWJF) contracted with Mathematica Policy Research and its subcontractor, the John W. Gardner Center for Youth and Their Communities (JGC) at Stanford University, to conduct a rigorous evaluation of Playworks. Twenty-five schools interested in implementing Playworks were randomly assigned to a treatment group that received Playworks in the 2010-2011 school year or to a control group that was not eligible to implement Playworks until the following year. The authors collected data from students, teachers and school staff in spring 2011 to document the implementation of Playworks and assess the impact of the program on key outcomes in six domains: (1) school climate, (2) conflict resolution and aggression, (3) learning and academic performance, (4) recess experience, (5) youth development and (6) student behavior. Ultimately, four additional schools will be added to the study and further analyses will be released. A description of study design and data sources. (Contains 4 exhibits, 15 tables and 2 endnotes.)