Objectives: The Collaborative Life Skills (CLS) program is a school-home intervention for students with Attention Deficit Hyperactivity Disorder (ADHD) symptoms and impairment. CLS integrates school, parent, and student treatments followed by booster sessions during a maintenance period into the subsequent school year. The program is delivered by school-based mental health providers. Beneficial post-treatment effects have been documented. This study evaluates effects of CLS after the maintenance period in the subsequent school year. Method: Using a cluster randomized design, schools within a large urban public-school district were randomly assigned to CLS (12 schools) or usual services (11 schools). Approximately six students participated at each school (N=135, grade range=2-5). Measures were completed at baseline, post-treatment, and follow-up during the next school year. Results: Students from schools assigned to CLS, relative to those assigned to usual services, showed significantly greater improvement at follow-up on parent, but not teacher, ratings of ADHD and oppositional defiant disorder (ODD) symptom severity, organizational skills, and global impairment. Within-group analyses indicated that parent and teacher-reported post-treatment gains for CLS in ADHD and ODD symptoms, organizational skills and academic competence maintained into the next school year. Conclusions: These results extend support for CLS to the following school year by demonstrating sustained benefits on parent-reported ADHD and ODD symptoms and functional impairment. The lack of significant teacher-reported differences between CLS and usual services highlights the need for further study of booster treatments for improving outcomes with new teachers across school years. [This paper was published in "Journal of the American Academy of Child and Adolescent Psychiatry" v57 p245-251 Apr 2018.]