That's not strictly true. The schools each have one time when mandatory attendance starts, and one time when mandatory attendance ends, but they all open their doors earlier, and close down later, when the student presence is still permitted. The bus schedules revolve around that 90% of kids that show up just for class and then leave for home afterward, but if there is a local need, it is usually technically possible to fill it. It just takes money. The problem is that the need and the money only rarely intersect.

Some school cafeterias even serve breakfast--mostly for kids with subsidized meals, who may not be able to eat regularly otherwise. That is state or federal money available to open earlier. Youth diversion program money can keep a school open later. It is entirely possible for a kid to be at school continuously for 12 hour intervals, every weekday, with no additional burden on the local taxes. Meanwhile, in the suburban schools, the clubs and extracurricular activities are powered by fees paid by the parents directly, and some kids get picked up and dropped off by private cars, as part of their parents' commutes, never even seeing the inside of a school bus.