Previous research has shown that insufficient sleep at night and daytime sleepiness contributes to psychological distress, cognitive deficiencies and poor academic performance. The current study examines the effect of nighttime sleep extension on sleep, psychological health, academic performance and cognitive functioning in a sample of adolescents with complaints of daytime sleepiness and insufficient nighttime sleep.Participants were 56 adolescents (34 females) aged 14 - 18 (Mean age = 16.46). Participants were given daily sleep diaries and actiwatch during an initial interview. Sleepiness, psychological, academic and cognitive assessments were completed after one week of sleep data collection. The participants were randomly assigned to either extend their sleep for at least 60 minutes on three consecutive school nights or continue with their normal sleep schedule. After the sleep extension the same battery of tasks were completed. Baseline and post-intervention sleep, psychological, academic and cognitive data included daily sleep diaries, the Pediatric Daytime Sleepiness Scale (PDSS), State Trait Anxiety Scale - Short (STAI-S), AIMS reading comprehension and mathematic questions, digit span, verbal fluency, trail making and go/no go inhibition.Nineteen of those assigned to extend their sleep succeeded (M = 80.35 min.). Repeated measures ANOVAs were performed on sleep, psychological well being, academics and cognitive assessments to evaluate the sleep extension intervention. Interactions for the sleep variables found that Sleep Extenders decreased difficulty in waking in the morning and daytime sleepiness, increased time in bed, total sleep time and sleep efficiency more than Non-Sleep Extenders, (all p < .05). No differences were found for the STAI-S or the academic questions. All participants improved on the forward digit span (p < .05); however, t-tests showed that only the Sleep Extenders improved on the backward digit span (p < .05). All participants performed worse on the verbal fluency task, (p < .01). Everyone improved on trail making part A (p < .01), however, only Sleep Extenders improved on trail making part B, (p < .01).Even small increases in the duration of nighttime sleep can improve sleep variables, reduce daytime sleepiness, and produce improvement on measures of cognitive ability requiring mental control and flexibility in adolescents.