We report findings from a 40 middle school randomized controlled trial of an adapted version of Coping Power (Lochman & Wells, 2002a) for middle schoolers, called the Early Adolescent Coping Power (EACP) Program (Bradshaw et al., 2019) to determine the impact of EACP on adolescents' mental health outcomes, as indicated by student self-reported and teacher-ratings on the Behavior Assessment System for Children (BASC). The EACP was implemented over the course of students' 7th grade school year. The sample included 709 students who were identified at baseline through a teacher screening process for aggressive behavior and enrolled into the project (69.8% African American and 59.4% male). For teacher-reported outcomes, intent to treat (ITT) results indicated that EACP was associated with a decrease in externalizing problems over time. Exploration of effect modification suggested that girls in the EACP condition demonstrated statistically significant decreases in School Problems over time, as well as a baseline by intervention effect whereby students and schools with greater baseline difficulties demonstrated decreased internalizing problems over time. For student-reported outcomes, there was a significant moderated effect, whereby girls in EACP demonstrated more favorable self-reported personal adjustment outcomes. Together, these results suggest that the early adolescent adaptation of Coping Power had preventive effects for 7th grade participants, and promotive effects specifically for girls, over time. [This paper was published in "Journal of School Psychology" v110 Article 101437 2025.]