A major concern has been busing. Even in normal times, districts use the same buses and drivers for students of all ages. They stagger start times to do that, with high schoolers arriving and leaving school earliest in the day. The idea is that they can handle being alone in the dark at a bus stop more readily than smaller children, and it also lets them get home first to help take care of younger siblings after school.
If high schools started as late as middle and elementary schools, that would likely mean strain on transportation resources. O'Connell said Nashville's limited mass transit compounds the problem.
We had four high schools in our city that used the school buses.
One started at 7, two started around 7:30ish, the fourth started around 8:30.
I was in the 8:30 school. We didn't like it because we didn't get out until 3:30, so all of the other high schools had been out for over an hour at that point. It was a point of rivalry contention between schools.
Where I'm from primary, middle, and secondary school are near each other, use the same busses & staggered start times, and we have no public busses. At least I see more bike racks now than when I attended!