Funny you should raise this. I read a study not that long ago that suggests that adolescents require more sleep than was thought before. Further, uniqueness in sleep patterns for this age group makes early morning risings, and feelings of tiredness till mid-morning very common.
Minimally they suggest 8 1/2 to 9 hrs sleep, but the internal *sleep clock* that we all have seems to be re-wired during these years which results in the individually only being able to fall asleep in the wee hours, and wake up later. All to do with the brains production of Melatonin, which happens differently for teens than adults.
Found a link: Have a go if you're interested.
http://www.kidshealth.org/teen/your_...uch_sleep.html
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