Another few reasons that I’ve heard for what’s opposing later high school start times are 1) due to limited numbers of buses, doing high school later would require the lower schools to be earlier, and parents don’t want their elementary schoolers out before sunrise, and 2) after-school activities like sports would be disrupted, both in an absolute sense (they already sometimes run pretty close to sunset) and a relative sense (a school that moved to a later schedule would either not be able to do sports games with other schools, or would have to have the athletes miss much more school than they already do in order to match the schedules of the other schools). To be clear, I do still think that the cost-benefit is clearly in favor of later starting.
Another few reasons that I’ve heard for what’s opposing later high school start times are 1) due to limited numbers of buses, doing high school later would require the lower schools to be earlier, and parents don’t want their elementary schoolers out before sunrise, and 2) after-school activities like sports would be disrupted, both in an absolute sense (they already sometimes run pretty close to sunset) and a relative sense (a school that moved to a later schedule would either not be able to do sports games with other schools, or would have to have the athletes miss much more school than they already do in order to match the schedules of the other schools). To be clear, I do still think that the cost-benefit is clearly in favor of later starting.