People at different ages have a different circadian rhythm. For teens and people in their early twenties it's a later rhythm. You can modify it, but it works to

People at different ages have a different circadian rhythm. For teens and people in their early twenties it's a later rhythm. You can modify it, but it works to varying degrees. There have been several studies that showed that high school for example should start later because of this. It's currently only ideal for teachers. Blaming this on a lack of sleep hygiene and discipline doesn't really address the problem. I'm not looking to any reference but a search should be trivial.