Background: Recess strategies that increase children’s physical activity and contribute to the daily 60 minutes of moderate to vigorous physical activity (MVPA) are recommended. Methods: A cluster randomized trial was conducted to examine the effect of supervised versus organized recess on children’s participation, physical activity, play, and social behavior. In supervised recess, children were free to play, and physical education (PE) teachers ensured safety. In organized recess, PE teachers provided challenging tasks. Data were collected using systematic observation. Children (N = 281; 8–10 y) from 14 schools received a 6-day parkour unit in PE and three opportunities to participate in a 20-minute parkour recess. Schools were randomized over a supervised and organized parkour recess condition. Results: The majority of children participated in parkour recess (range = 56%–85%), with more boys participating in all 3 organized versus supervised recess sessions (57% vs 35%, P = .01). Boys spent more time in MVPA during organized recess (79% vs 71%, P = .02). Boys and girls spent more time in activity games during organized recess (59% vs 46%, P = .01; 59% vs 47%, P = .001). Conclusion: Organized recess attracted more children and made the largest contribution to daily MVPA.