Starting school later allows kids to sleep more. Research indicates that "“[a] loss of one hour of sleep is equivalent to [the loss of] two years of cognitive maturation and development." With high school kids, the correlation between additional sleep and higher grades is even more pronounced. But schools continue to start high school classes before eight in the morning. Why? One popular answer seems to be extracurriculars: earlier start times allow more after-school practice hours.
A kid who doesn't sleep properly is functionally equivalent to a kid with lead poisoning. But who cares as long as the football team goes all the way?
Then again, what do I know? I'm just a bitter, unsporty former high schooler who had to get up at 5:30 (5:00 on ROTC days) to catch a 6:15 bus to my first class at 7:30.