Background: High volumes of school-based sedentary time may impact academic achievement and executive function negatively. This study evaluated a multimodal classroom program's (POWER) effect on fifth graders' physical activity (PA) and executive function. Methods: Six 5th grade classes (3 = intervention [POW]; 3 = waitlist control [CONT]) in 2 diverse New Jersey schools participated. Data were collected before, during, and post-intervention. PA was assessed via accelerometer, executive function by NIH Toolbox, and academic achievement via standardized math tests. The POW principal, teachers, and select students participated in follow-up interviews. Group comparisons were made by multivariate repeated-measures ANOVA and linear regression. Results: PA decreased in both groups over time, but POW's post-intervention class-time PA was significantly higher than CONT's. POW's NIH Toolbox score increased 3 percentiles more than CONT's. Intervention fidelity was associated with significantly higher scores for one NIH Toolbox test. Student math test scores increased significantly for both schools, but there was no significant main effect for group. POW's feedback was positive, with the principal reporting fewer disciplinary referrals and teachers and students conveying positive growth. Conclusions: Overall, POW's positive changes and the favorable reception of POWER support POWER'S ability to improve children's socioemotional and physical health.