 Starting school before 8.30? Results in worse grades. In Seattle, they moved the start time from 7.50 to 8.45, and they saw a 4.5% increase in the student's median grades. Starting middle and high school later is more aligned with how your body clock works. When you go through puberty, your circadian rhythm shifts. So by nature, you go to sleep later and wake up later than usual. Only 22% of U.S. teens get at least eight hours of sleep at night. The good news? California schools will be starting at 8.30 from now on, and a few other states have proposed bills to do the same.