Early childhood mental health consultation (ECMHC) has been promoted by the federal government as a promising model for reducing early childhood expulsions and suspensions and is now implemented by numerous states. Despite growing ECMHC proliferation, this study is only the second randomized controlled trial of ECMHC, extending the methodologies of the first to include assessment of effects on random peers. Classrooms were assigned randomly to treatment or waitlist-control condition (n = 51 classrooms, 57 preschool teachers, and 190 preschoolers). Evaluation measures were collected at both pretreatment and posttreatment, following approximately six consultation visits. Classroom and teacher outcomes were evaluated with ordinary least squares regressions, while hierarchical linear modeling was used to evaluate child-level outcomes, accounting for the nested study design. Treatment children (both the target children who prompted the referral for ECMHC and random peers) evidenced significant improvements in social and emotional skills. Promising trend findings were noted for child behavior problem reduction and teacher pedagogical approach and locus of control. No significant effects were found on likelihood of expulsion and classroom mental health climate. This is the first ECMHC to demonstrate effects on nontarget peers in a rigorous randomized controlled trial. Programmatic and methodologic limitations and implications are discussed.