Background: With the growing need for children from underserved populations to be physically active it is imperative to create developmentally appropriate and enjoyable physical education programs that promote physical activity. The purpose of this study was to determine the effects of mastery and performance climates on physical activity during physical education. Methods: Children (N = 108) in grades K-2 from a rural southeastern elementary school in the United States were randomly assigned to a mastery- or performance-oriented climate. The climates were implemented over 10 school days during regular scheduled physical education classes, and physical activity was measured with pedometers and system for observing fitness instruction time (SOFIT). Two experts in mastery motivational climates served as teachers for the study and were counterbalanced between conditions. Results: Results showed that steps/minute were significantly higher for the mastery condition, and participants in the mastery condition spent significantly less time sitting (p less than 0.001) and in management (p less than 0.001) and more time in moderate-to-vigorous physical activity (MVPA; p = 0.002) and fitness activities (p = 0.001). Conclusion: Results indicate that a mastery approach, which allows children the opportunity to drive their own physical activity, elicits higher step counts and more time spent in MVPA compared with a performance-oriented approach. (Contains 3 tables.)