Objective This meta-analysis evaluated the efficacy of behavioral classroom programs on symptoms of Attention-deficit Hyperactivity Disorder or Oppositional Defiant and/or Conduct Disorder in primary school children. Method Online database searches (in PubMed, Embase, Psycinfo, and Eric) yielded nineteen randomized controlled trials (N = 18,094), comparing behavioral classroom programs (including multimodal programs involving a classroom program) to no treatment/treatment as usual. Random-effects meta-analyses were conducted for teacher-rated and classroom-observed disruptive classroom behavior and for classroom-observed on-task behavior. Post-hoc analyses investigated whether effects depended on type and severity of problem behavior. Meta-regressions studied the moderating effects of age, gender, and intervention duration. Results Small positive effects were found on teacher-rated disruptive behavior (d = -0.20) and classroom- observed on-task behavior (d = 0.39). Program effects on teacher-rated disruptive behavior were unrelated to age, gender, type and severity, but negatively associated with intervention duration (R2 = 0.43). Conclusion Behavioral classroom programs have small beneficial effects on disruptive behavior and ontask behavior. Results advocate universal programs for entire classrooms to prevent and reduce disruptive classroom behavior.