Examine the effects of active video games (AVGs) on children's school-day energy expenditure (EE) and physical activity (PA)-related self-efficacy, social support, and outcome expectancy over 9 months. Participants were 81 fourth grade students ( X ¯ age = 9.23 years, SD = 0.62; 39 girls) from two urban Minnesota elementary schools. A once-weekly 50 min AVG intervention was implemented in the intervention school for 9 months in 2014-2015 while the control school continued regular recess. Children's school-day EE (daily caloric expenditure) and mean daily metabolic equivalent (MET) values were estimated via accelerometry whereas self-efficacy, social support, and outcome expectancy were assessed with psychometrically-validated questionnaires. All measures were completed at baseline and at the 4th and 9th months. We observed significant interaction effects for daily caloric expenditure, (1, 58) = 15.8, < 0.01, mean daily MET values, (1, 58) = 11.3, < 0.01, and outcome expectancy, (1, 58) = 4.5, < 0.05. Specifically, intervention children had greater increases in daily caloric expenditure (91 kilocalorie/day post-intervention group difference), with control children decreasing daily caloric expenditure over time. We observed identical trends for mean daily MET values (0.35 METs/day post-intervention group difference). Interestingly, we observed outcome expectancy to increase in the control children, but decrease among intervention children, at post-intervention (1.35 group difference). Finally, we observed a marginally significant interaction effect for social support, (1, 58) = 3.104, = 0.08, with an increase and decrease seen in the intervention and control children, respectively. We observed no interaction or main effects for self-efficacy. Observations suggested an AVG intervention contributed to longitudinal increases in school-day EE and social support compared to the control condition. Future research should examine how self-efficacy and outcome expectancy might be promoted during school-based AVG interventions.