The primary purpose of the present systematic review and meta-analysis was to review systematically and then meta-analyze evidence on the effects of classroom[1]wide social–emotional interventions for improving the social, emotional, and behavioral outcomes of preschool children when compared with either a no-treatment control group or business-as-usual group. The secondary objective was to use moderator analyses to identify specific study characteristics that were associated with larger effect sizes across the social, emotional, and behavioral outcomes. Specifically, three research questions guided this systematic review and meta-analysis: Research Question 1: What were the attributes of study participants and interventions involved in the review? Research Question 2: Did classroom-wide social– emotional interventions yield statistically significant and noteworthy mean effects for preschool children’s social, emotional, and behavioral outcomes? Research Question 3: Did select study or intervention characteristics moderate obtained intervention effects? (author abstract)