A lot of kids are severely and chronically sleep-deprived as a result of early school starts that conflict with their natural sleeping patterns. Teenagers in particular tend to most alert in the evening and night, and it's not a matter of refusing to go to bed; they're biologically programmed to be awake at those times and getting up at 6am to get to school for a 7am start 5 days of the week is as damaging to their health as it would be if someone woke up an adult with what's considered a 'normal' sleeping pattern at 2am for 5 days of the week every week and demanded they go to work. A person's natural waking and sleeping times vary through their life, with the time they fall asleep and wake up getting gradually later and later through their teens and then reversing and gradually becoming earlier again as they go into their 20's and 30's. Different individuals are also shifted earlier or later, with some people waking early and being active in the mornings and some people waking later and being active in the evenings, but school shoe-horns everyone into an extreme early-morning schedule.
