[kingbirdy]

You're missing two things, one for each age group:

For the younger kids, each hour earlier they start is an hour earlier they finish, which means parents need to either finish work earlier (not possible for most people), or pay for an additional hour of after-school child care (expensive). Having free child care to cover the gap between school finishing and work finishing is extremely rare, and the acceptable age to leave your child unattended after school is going up due to over protective parenting (for example, I was a latchkey kid starting in the 3rd grade, but nowadays that seems almost unheard of until middle school).

For the older kids, starting later means sports / extracurriculars finish later, potentially after dark or after the parents are done working and expect kids to be coming home.

[crazygringo]

Definitely can see what you mean about the younger kids in the afternoon, thanks -- I'd definitely been missing that in my thinking.

Funny I never thought about it till now -- in my public elementary school back in the day, the (minority of) kids who didn't have a parent at home in the afternoon, stayed an extra 2-3 hours at school for the rest of the afternoon at no charge, mainly doing art activities like finger painting etc, and they even provided snacks. I remember joining a few times just because I wanted to hang out with my friends there. It was very minimally structured/supervised -- just something to do to maintain interest but not be rowdy, not intended to be "educational" or anything.

I've never heard of that kind of thing since though. But it sure makes a lot of sense for that to be provided standard by elementary schools, now that 2 working parents is the norm.