This prospective longitudinal study evaluated the impact of daytime sleepiness on the school performance of 62 college students diagnosed comprehensively with attention deficit hyperactivity disorder. The primary goal of the study was to determine if self‐reported daytime sleepiness rated at the beginning of the academic year could predict academic and overall functioning at the end of the academic year while also considering potentially important covariates, including symptoms of inattention, hyperactivity and impulsivity, medication status and whether or not students lived at home or on‐campus. Self‐reported daytime sleepiness predicted longitudinally school maladjustment, overall functional impairment and the number of D and F grades (i.e. poor and failing) students received in courses above and beyond both self‐ and parent‐report of symptoms, but did not predict overall grade point average. Living at home served as a protective factor and was associated with less school maladjustment and overall impairment. Gender was the only significant predictor in the overall grade point average model, with female gender associated with higher overall grades. The implications of these findings for monitoring and treatment of sleep disturbances in college students with attention deficit hyperactivity disorder are discussed.