The current study aims to evaluate the effectiveness of a high-intensity (HI) versus a low-intensity (LI) skills-based summer intervention delivered to adolescents with ADHD by school staff in improving depressive symptoms, anxiety symptoms, social problems, and self-esteem. Participants were 325 ethnically diverse rising sixth and ninth graders with ADHD randomized to an HI versus an LI intervention (n = 218) or recruited into an untreated comparison group (n = 107). Group x time and group x grade x time one-year outcome trajectories were compared using linear mixed models. Across the transitional year (sixth or ninth grade), adolescents in the HI group were found to experience significantly greater decreases in depressive symptoms (p = .022, d = .25) compared to the LI group. There was no significant impact of the HI intervention (vs. LI) on anxiety symptoms (p = .070, d = .29), social problems (p = .054, d = .34), or self-esteem (p = .837, d = 0.21); however, secondary analyses of the non-randomized untreated comparison group indicated a significant effect of HI versus the untreated comparison group on social problems (p = .009, d = 43). These significant treatment effects suggest that comprehensive academic and organizational skills interventions for adolescents with ADHD may have a secondary impact of relieving adolescent depression for teens with this comorbidity. Given mixed evidence for the efficacy of the HI intervention on social skills, future work should further evaluate this effect.