The present study developed and tested a theoretical model examining the inter-relationships among sleep duration, sleep quality, and circadian chronotype and their effect on alertness, depression, and academic performance. Participants were 385 adolescents aged 13-18 years (M = 15.6, SD = 1.0; 60% male) were recruited from eight socioeconomically diverse high schools in South Australia. Participants completed a battery of questionnaires during class time and recorded their sleep patterns in a sleep diary for 8 days. A good fit was found between the model and the data (χ(2)/df = 1.78, CFI = .99, RMSEA = .04). Circadian chronotype showed the largest association with on adolescent functioning, with more evening-typed students reporting worse sleep quality (β = .50, p < .001) and diminished alertness (β = .59, p < .001). Sleep quality was significantly associated with poor outcomes: adolescents with poorer sleep quality reported less sleep on school nights (β = -.28, p < .001), diminished daytime alertness (β = .33, p < .001), and more depressed mood (β = .47, p < .001). Adolescents with poor sleep quality and/or more evening chronotype were also more likely to report worse grades, through the association with depression. Sleep duration showed no direct effect on adolescent functioning. These results identified the importance of two lesser-studied aspects of sleep: circadian chronotype and sleep quality. Easy-to-implement strategies to optimize sleep quality and maintain an adaptive circadian body clock may help to increase daytime alertness, elevate mood, and improve academic performance.