Adolescents with attention-deficit/hyperactivity disorder (ADHD) are at heightened risk of experiencing academic difficulties due to organizational deficits. Impairment can be exacerbated through poor sleep hygiene and excessive daytime sleepiness, prevalent sleep challenges for adolescents with ADHD. Given established relationships among sleep, memory consolidation, and executive functioning, sleep hygiene and daytime sleepiness may affect academic and organizational treatment outcomes. The current study examined the influence of pre-treatment daytime sleepiness and sleep hygiene on academic and organizational treatment outcomes in a randomized controlled trial of a multicomponent intervention for 171 high school students with ADHD. Participants were assigned to either the treatment group (n = 85, Mage = 15.0, SD = 0.8, 80% male, 71% White/Non-Hispanic) or the control group (n = 86, Mage = 15.1, SD = 0.9, 78% male, 87% White/Non-Hispanic). Multiple regression analyses with an interaction term were conducted, finding significant main effects for poor pre-treatment sleep hygiene and excessive daytime sleepiness predicting worse post-treatment GPA, organizational skills, academic problems, and homework problems. A significant moderation effect was found such that greater pre-treatment daytime sleepiness was associated with more post-treatment homework problems, but only for the control group. Incorporating efforts to improve sleep hygiene and daytime sleepiness in interventions for adolescents with ADHD may enhance treatment-induced improvements. Future studies should utilize objective sleep measures to gain greater understanding of sleep’s impact on adolescents’ response to psychosocial treatment.