Mammele: The very Chasidish mosdos typically charge a pittance in tuition when compared to Litvish mosdos. (Forget about the arm and leg charged by MO schools.) It would seem unlikely tuition would cause this among Chasidim. That leaves housing. Is housing costs really quantifiably affecting family size in KJ and NS?
While on topic, in your estimation what are the ranges and what are the averages for family size (for families completed bearing children) between the various neighborhood/locations, progressiveness and groups?