Lots of things change at puberty. According to a report in Archives of Pediatrics & Adolescent Medicine, one of those changes may be a brand new sleep-wake scenario. Adolescents seem to gravitate toward falling asleep and waking up to two hours later than they did in childhood.
"Judith A. Owens, M.D., M.P.H., of the Hasbro Children's Hospital, Providence, and colleagues, studied 201 students in grades 9 through 12 attending an independent high school in Rhode Island. For the purposes of the study, class start time was delayed 30 minutes, from 8 a.m. to 8:30 a.m. Additionally, students were required to complete the online retrospective Sleep Habits Survey before and after the change in school start time."
This later start in the day brought greater satisfaction to students in terms of sleep and better motivation. They were less sleepy and lethargic during the day. Initially, the school staff was against the change to a later class start time but later were in favor of making the change permanent. The students were also highly supportive of such a change.
http://www.sciencedaily.com/releases/2010/07/100705190532.htm