HSS, is it possible that many of the 900 from Flatbush (where there are plenty of other schools) and those from other areas than BP, choose to travel to BYOBP because they get a good deal there?
It happens to be a very well run school, but there are other very well run schools in Brooklyn. Rabbi Shapiro claims his tuition is lower than most Bais Yaakovs. That has to be at least part of the attraction.