The following article originally appeared in The Harvard Education Letter (volume 24, number 6). Copyright 2008 President and Fellows of Harvard College. All rights reserved.

Since the early days of Head Start, the debate has raged over public support for early childhood education, with the federal government deciding more than four decades ago to back programs that support the children of low-income families.

Today that debate has shifted to municipalities and states, where advocates for universal preK urge public funding for all three- and four-year-olds whose parents want to send them. Others, meanwhile, argue that with scarce public dollars, the funding should be focused on low-income preschoolers.

Bruce Fuller, professor of education and public policy at the University of California at Berkeley, maintains that research has yet to show that middle-income children receive long-term benefits from preK education and, therefore, public funding of preschool should be aimed at helping low-income youngsters where the benefits are backed by a more solid body of research. “While it’s clear that quality preschool can provide a sustained boost for the children of poor families, it doesn’t give much of a bump for the children of the middle class,” says Fuller, author of Standardized Childhood: The Political and Cultural Struggle over Early Education.

Fuller says that a range of studies show gains for low-income students through early childhood education. There’s the Perry Preschool study, for example, the earliest and most widely recognized study to find substantial benefits for low-income students as they moved through public school and into adulthood. The study found Perry graduates about 20 percent more likely to have graduated from college, less likely to be arrested, and, among girls, less likely to experience teen pregnancy. The Chicago Child-Parent Center’s longitudinal study of 1,549 low-income children who entered kindergarten in 1985 also showed promising results. So did the Carolina Abecedarian Project, which provided intensive instruction to 111 low-income children.

But Fuller and Susannah Loeb, who analyzed the Early Childhood Longitudinal Survey of 22,000 kindergarteners nationwide, found that any benefit to middle-class children largely faded out by third grade. That same study found sustained gains for poor children. “The effects wash out for middle-income kids,” says Fuller.

He suggests that proponents of universal preK overstate the achievement gains of middle-class students in their effort to shape public opinion and sway policymakers. He believes that middle-class four-year-olds who don’t attend preK are ready for school because they grow up in enriched homes, where parents take on the role of teachers.

The cost of universal preK can be high. California voters in 2006 defeated a proposition that would have boosted income taxes on individuals earning more than $400,000 to pay for a proposed $2.3 billion universal preK program for every four-year-old in the state. Fuller says more than half the program would have paid for preK for middle- and upper-middle-class parents who already send their children to private preK programs.

“Let’s continue to focus scarce public resources on expanding preschool in poor communities,” says Fuller. “Let’s not blow out these scarce dollars on a universal entitlement.”