I heard this first in When, but here is another article talking about how we have early start school times and they’re not the best for kid’s learning.
American teenagers are chronically sleep-deprived. As children enter puberty, physiological changes delay the onset of sleep and make it more difficult to wake up early in the morning. By the end of middle school, there is a large disconnect between biological sleep patterns and early-morning school schedules: one study found that students lose as much as two hours of sleep per night during the school year compared to the summer months, when they can better control their sleep schedules.
I find it hard to see any other conclusion outside we do this because it’s easiest for adults and work.