[lodrein]

It may seem feasible on the long run. Indeed, it can be easier for the parents of the new children to adapt their schedule.

But it can be very hard for the parents that previously chose the school (partly) because of its start time, and adapted their own life & work schedule around this time.

[kidofthestreets]

A "two-tier" system with 7:30 and 9:00 starts is interesting - one thing to consider, though, is that many, many families in Boston would like for school to start between 8:00 and 8:30. So a solution with zero students starting in this window might be unpopular.