Treating ADHD with medications alone is often ineffective, but adding other methods, such as behavioral treatments, may be beneficial. Researchers have developed a psychosocial treatment for adolescents with ADHD, called the Challenging Horizons Program (CHP), that is delivered in school and targets social impairment, family conflict, and academic failure. Two versions of CHP were developed, an after-school model and a consultation model. The after-school model involves 2 to 3 days of individualized treatment per week and has a higher cost than the consultation model because it involves hiring specialized counseling staff and finding space to house the program after school. The consultation model involves teaching CHP intervention strategies to school staff, who then mentor students with ADHD and deliver interventions as needed to solve problems. This model is less expensive, but it does not deliver treatment as often or consistently as the after-school model. This study will compare the after-school and consultation models of the CHP to determine their relative efficacy and cost effectiveness. The study will also evaluate factors that may predict which adolescents would benefit most from either of the two models.