Why don't schools simulate a typical 9 to 5 work week for students and remove homework entirely?
I know this is typical for the US so this is more for US people to respond to. I wouldn't say that it is the best system for work, just wondering about the disconnect.
I'm not sure if adding more time in school would be helpful even if there's no homework. I have a 9-5 job, and by 3:30 I'm already mentally checked out for the day, just watching the ole clock tick slowly to five. Not to mention that kids aren't paid to go to school, so the kids wouldn't see any tangible benefits of a longer day. In theory they would learn more, but most kids aren't thinking that way and there's only so much a kid can learn in one day anyway.
When I was in high school, they added 25 minutes to every day to build in snow days. If we did not use them, school just ended earlier than scheduled. This could serve basically the same function, to shorten the school year.
However, that's not even necessarily a good thing for learning... I think year-round school is generally accepted to be the best way to learn having many shorter gaps rather than one long summer. I suppose it could build in an extra week or two of breaks normally not present in a year-round school schedule.