While children in the program showed some positive results on measures of cognitive skills and social/behavioral ratings while in the program, those results lasted only so long as the children were enrolled and did not carry through to kindergarten or early elementary school. The principle positive effect noted in the HSIS was in social skills for 3-year-olds, but these results were reported only by parents and not replicated by outside examiners. Teachers, by contrast, noted a negative effect on social/emotional skills for the 4-year-old cohort.
The point of Head Start is the promise that it offers poor children a leg up and prepares them for school. It would be nice if it worked, but it doesn't. It does provide jobs for teachers and federally subsidized day care. But taxpayers have spent $180 billion since 1965 for a program that fails to achieve its objectives.
Other studies have examined the effect of preschool more generally on school performance and have found effects ranging from very small to none.
What then was Obama referring to when he insisted that "high-quality" preschool "boosts graduation rates," "reduces teen pregnancy" and so forth? In a post titled "Obama's Preschool Proposal Is Not Based on Sound Research" on the center/left Brookings Institution website, Russ Whitehurst explains that the studies the president and other advocates of universal pre-K rely on are flawed. They do not involve randomized controls (as the HSIS did) but instead employ something called "age-cutoff regression discontinuity."
Due to state-mandated birthdates for enrollment in preschool, the studies wind up comparing kids who are actually enrolled in play-based programs for 3-year-olds with those enrolled in academically oriented preschool for 4-year-olds. These regression discontinuity studies also fail to account for dropouts from the program. The Brookings post, to which Armor also contributed, concludes: "Because 'gold standard' randomized studies fail to show major impacts of present day pre-K programs, there are reasons to doubt that we yet know how to design ... a government funded pre-K program that produces sufficiently large benefits ... "
Armor and Souza suggest in National Affairs that those truly respectful of science would propose: "A national demonstration project for pre-K in a selected number of cities and states, accompanied by a rigorous randomized evaluation that would follow participants at least into the third grade. This demonstration project should also examine whether 'preschool for all' closes achievement gaps between rich and poor, since it is possible that middle-class children will benefit more than disadvantaged children."
This would put science in its "rightful place," but don't hold your breath. Many liberal nostrums are impervious to evidence.