Are you a morning person? Your teenager is probably not. Adolescents tend to prefer going to bed later and waking up later than children and adults. This shift in sleep patterns during adolescence may drive parents to distraction, but now we know that it also impairs academic performance if teens are required to wake early for classes. A study of 60 high school seniors in advanced-placement biology kept a log of their sleep prior to the start of the school year and then during the year. Compared to their sleep patterns in August, students typically lost up to 2 hours of sleep per night during the weekdays of the school year. Students' performance on standardized vigilance testing was significantly worse in the mornings than in the afternoons, and students in early morning classes reported feeling weary and less alert than at other times of the day. We know that the production of the hormone melatonin is delayed in teens, making it harder for them to fall asleep. This makes for groggy, passive, sleep deprived students. The researchers suggested that classes for adolescents might serve them better if school started later (fat chance). They also offered that if standardized testing began at 10:00 rather than 8:00 scores would probably improve.

Reference:

Hansen M, et al. The impact of school daily schedule on adolescent sleep. Pediatrics June 2005; 5(6):1555.