The holiday and school-term sleep patterns of 310 Australian senior school students were surveyed in a longitudinal study, along with self-reported sleep quality, mood, daytime functioning, grades and circadian preference. Evidence was found that with the impact of school schedule, students accrued a significant sleep debt, obtaining insufficient sleep for their needs and reporting lowered mood and daytime functioning. Support was found for the hypothesis that trait circadian preference mediates mood, daytime functioning and academic grades through its effect on sleep variables at school time. It was concluded that while the imposition of school schedule negatively impacted on mood and daytime functioning for the sample as a whole, evening-oriented adolescents were the most vulnerable to poorer outcomes. These students obtained poorer quality and less sleep than morning-oriented students. Sleep factors impacted negatively on evening-oriented students’ mood and ability to function at school during the day, which in turn predicted poorer academic achievement.