In 1997-98, Minneapolis moved the high school starting time from 7:15 to 8:40. St. Paul did not. Now Minneapolis and St. Paul are otherwise pretty similar. (Pace Garrison Keillor.) Hinrichs compared ACT scores in the Twin Cities before and after the change in Minneapolis. If extra sleep helps teenagers you’d expect scores to improve in Minneapolis relative to St. Paul.
Nope. Nada. No detectable difference.