I still remember the parents' orientation session when my son started Kindergarten at our Rich Suburban, Lilly-white public school district (1988). The principal wanted to reassure the parents whose kids had not gone to private pre-schools (my son had had 3 years of it by then). He assured them that by December of that year, there would be absolutely no difference in academic performance between the pre-schooled kids and those who stayed home with (presumably) Mommy.
And so it goes. "Head-Start" provides free babysitting, lots of jobs for otherwise-unemployable teachers and child care workers, and makes liberal politicians feel like they are doing something nice for "disadvantaged" yoot. What more could anyone ask?