A growing body of research has documented a link between variation in implementation dosage and outcomes associated with preventive interventions. Complier Average Causal Effect (CACE; Jo in J Educ Behav Stat 27:385-409, 2002) analysis allows for estimating program impacts in light of variation in implementation. This study reports intent-to-treat (ITT) and CACE findings from a randomized controlled trial (RCT) testing the impacts of the universal PAX Good Behavior Game (PAX GBG) integrated with Promoting Alternative Thinking Strategies (i.e., PATHS to PAX) and PAX GBG only compared to a control. This study used ratings by 318 K-5 teachers of 1526 at-risk children who, at baseline, were rated as displaying the top 33rd percentile of aggressive-disruptive behavior. Leveraging a prior study on these data (Berg et al. in Admin Policy Ment Health Ment Health Serv Res 44:558-571, https://doi.org/10.1007/s10488-016-0738-1 , 2017), CACE was defined as the effect of intervention assignment for compliers, using two compliance cut points (50th and 75th percentile), on posttest ratings of student academic engagement, social competence, peer relations, emotion regulation, hyperactivity, and aggressive-disruptive behavior. The ITT analyses indicated improvements for students in the integrated condition on ratings of social competence compared to the control condition. The CACE analyses also indicated significant effects of the integrated intervention on social competence, as well as academic engagement and emotion regulation for students in high compliance classrooms. These findings illustrate the importance of considering variation in implementation within the context of RCTs.