Just a tidbit of information: studies show that bumpy the time children are in 3rd grade, there is no difference in performance between those who attended preschool and those who didn't. Similarly, the same holds true for kindergarten. Early learning in the government schools is not a contributing criteria to future success.
if pressed, I would say that early learning has little to no effect on the at-risk status of children either. That risk comes largely from the home dynamics which don't change just because the kid went to school at age 4 instead of at age 5 or 6.
It's nothing more than "free" daycare given in the name of "educating" the kids.