During puberty, youth undergo a shift in their circadian clocks that makes it harder for them to fall asleep until later in the night. Meanwhile, they can stay awake longer before experiencing an increase in the pressure to sleep
https://www.apa.org/topics/children/school-start-times
https://www.washington.edu/news/2018/12/12/high-school-start-times-study/
More to the original point, you don’t need a bunch of scientists with lab coats and clipboards to tell you teenagers don’t sleep well on an early schedule, you could just ask one. Not to mention the homework load etc…