Cognitive-behavioral interventions (CBIs) are effective in decreasing externalizing behavior in school-aged children. To ensure that CBIs meet the needs of a diverse student population, it is important to examine whether intervention effectiveness is influenced by characteristics common to students identified with problem behaviors. In this study, we used structural equation modeling to examine whether the effectiveness of Tools for Getting Along, a school-based, universally delivered CBI, was moderated by student race, socio-economic status, and/or levels of anger control prior to intervention, and whether post-intervention anger levels served as a mediator of the intervention effects. Findings suggested that race and socio-economic status did not moderate intervention effectiveness, but effects on externalizing behavior were moderated by levels of anger control prior to intervention. Findings also indicated that post-intervention anger control levels did not mediate intervention effects. We discuss the limitations of our study, along with implications for research and practice.