Background: Children from low-income and racial/ethnic minority backgrounds are more prone to insufficient physical activity and heightened sedentary behaviors. This study aims to increase moderate to vigorous physical activity and decrease sedentary behaviors among high-risk children through an inclusive and transformative sport skill development physical education (PE) intervention., Methods: Elementary school-aged children were recruited from 3 public schools located in underserved communities in Houston, TX. Classrooms were randomly assigned to a sport-based PE class (intervention, 12 classrooms, n = 124) or a standard PE class (control, 13 classrooms, n = 133). The intervention was implemented at school by teachers over 10 weeks, whereas at home, the intervention group received equipment, virtual classes, and parent trainings. Activity behaviors were assessed using accelerometry (ActiGraph GT3X+) at baseline and post intervention. Multilevel linear mixed-effects models were conducted to examine changes in activity behaviors between the study conditions., Results: Participants were 9.33 (0.68) years old, and 46% were females, who identified as either Hispanic/Latino (48%) and/or Black (38%). The difference in minutes of weekend sedentary behavior change was 32 minutes between study conditions (P = .012). Specifically, intervention girls decreased weekend sedentary behavior by 37 minutes, whereas girls in the control condition increased by 8 minutes (P < .01). Despite the direction of change in overall, weekday, or weekend moderate to vigorous physical activity and overall or weekday sedentary behaviors in favor of the intervention, these effects did not reach the statistically significant level compared to the control condition., Conclusions: Sport-based PE intervention can be an important strategy to decrease child sedentary behaviors during out-of-school periods, particularly among girls.