The first studies showing Head Start to be a complete waste of money came out back in the early seventies.
we adopted our sons through the county... our oldest son had been in Head Start as a foster child... he was about to enter kindergarten... he could count to 2, he knew no colors, and two shapes... he knew none of the alphabet... we talked with his teachers and asked them why??? one of them said they were mostly concerned with nutrition... once he came to live with us, he stopped headstart... by the end of the first month he knew the alphabet, basic shapes and colors and could count to 14... within 7 months, he was reading... i homeschool him and his younger brother..,
The truth of Head Start is that it was designed as a jobs progam (Redistributionism) for unemployable underclass mothers who got "hired" as "classroom aides" at HS progams, and basically sat around chatting and picking their noses while their kids played with whatever toys were provided.
It never was expected to make any difference for the kids, all it was for them was group babysitting.