Background: The after-school period is potentially an important venue for increasing physical activity for youth. We sought to assess the effectiveness of the Sports, Play, and Recreation for Youth (SPARK) program to increase physical activity and improve cardiorespiratory fitness and weight status among elementary students after school. Methods: This quasi-experimental controlled study compared change in moderate to vigorous physical activity (MVPA), body mass index (BMI) z-score, and cardiorespiratory fitness (VO[subscript 2]) over 5 months between students in after-school programs exposed to SPARK versus controls. Participants were fifth grade students at 3 intervention schools (N = 48) and 3 control schools (N = 52). Results: There was no difference between groups in mean change in MVPA, BMI z-score, or cardiorespiratory fitness. After-school time dedicated to physical activity did not increase with the implementation of SPARK. Intervention students' self-assessment of their activity levels relative to their peers significantly increased compared to control students (p = 0.011). Conclusions: In this 5-month study, the SPARK program did not increase MVPA in the after-school setting. Increasing the amount of time dedicated to physical activity may be as important as the curriculum used to effectively increase physical activity after school. (Contains 3 tables.)