> Since the whole getting kids to school early so that someone can watch them while the parents work only really only applies to younger students, this isn't a problem.

I'd guess that a significant fraction of teenagers would have difficulty waking up and getting to school on time if they didn't have a parent around to wake them up, feed them breakfast, push them out the door, etc. Not all teens are self-motivated and independent enough to do this on their own every single day.