Engagement in aggressive behavior has been associated with many negative outcomes for children including academic failure, social maladjustment, peer rejection, and lifelong destructive and criminal behavior. Cognitive-behavioral interventions (CBIs), which use behavioral principles, behavior therapy, and cognitive mediation through self-talk, are one type of intervention used to decrease aggressive behavior in school populations. The purposes of this meta-analysis are to examine the effectiveness of school-based CBIs in reducing or preventing aggression in children and youth, to explore the effectiveness of interventions that used school personnel compared to those that used study personnel as CBI implementers, and to determine the effectiveness of CBIs delivered universally compared to those that are delivered in small group settings. We identified 25 articles meeting our inclusion criteria and found a mean effect size (ES) of - 0.14, (SD = 0.48) and a mean weighted ES score of - 0.23. Results showed that the universal intervention delivery method had a significant influence on the magnitude of the effect size ( F(1, 61) = 4.84, p = .032). In light of these results we discuss study limitations and suggest future research on potential CBI moderators and the role of CBI in the current school environment.