From the book Why we sleep, by Matthew Walker, it's reported that teenager's circadian rhythm is different from the one of their younger siblings. It's shifted progressively forward, so forward that it passes even the timing of adults.
This is something wired in their brain and should be addressed when setting school times.
Moreover, Walker also proposes a socio-evolutionary explanation of why adolescent sleep schedule is shifted:
"Central to the goal of adolescent development is the transition from parental dependence to independence, all the while learning to navigate the complexities of peer-group relationships and interactions.
One way in which Mother Nature has perhaps helped adolescents unbuckle themselves from their parents is to march their circadian rhythms forward in time, past that of their adult mothers and fathers.
This ingenious biological solution selectively shifts teenagers to a later phase when they can, for several hours, operate independently—and do so as a peer-group collective.
It is not a permanent or full dislocation from parental care, but as safe an attempt at partially separating soon-to-be adults from the eyes of Mother and Father. There is risk, of course. But the transition must happen. And the time of day when those independent adolescent wings unfold, and the first solo flights from the parental nest occur, is not a time of day at all, but rather a time of night, thanks to a forward-shifted circadian rhythm."
edit: putted a little more space in between sentences