Accumulating research has identified family behavioral interventions as an empirically supported psychosocial treatment for students with attention deficit hyperactivity disorder (ADHD). The mechanisms behind the effectiveness of these interventions, however, have been less well studied. The current study examined possible mediators of improvement in 181 children's homework performance as a result of a family-school intervention for children in Grades 2-6 with ADHD (Family-School Success program, FSS). Specifically, changes in parenting practices and the family-school relationship were examined as potential mediators of the relationship between FSS treatment and improvements in students' homework performance. When we controlled for pre-treatment levels of behavior and demographic variables, reductions in negative parenting practices were associated with both parent and teacher reports of homework performance at post-treatment. The relationship between treatment group and teacher reports of homework responsibility was fully mediated by reductions in negative parenting practices. Although the meditational effect for parent reports of homework problems did not meet criteria for full mediation, the magnitude of the treatment effect was significantly altered by reductions in negative parenting. This study replicated findings linking reductions in negative parenting to improvements in child behavior and extended findings to homework performance.