Did BPS consider applying the changes to only one or
a few high schools and their feeder schools? Perhaps
the realities of distribution of students among schools
in Boston not allow doing such a beta test?
That could be a way to do it, and Boston decided to do it all at once. I think their reasoning was the fairness of the process (it's hard/unfair to use beta testing on public schools). Also, it is such a hard change that maybe it is easier to do it all at once. You may also want to consider the political implications that are very important when making this kind of decisions.