Barack Obama says he believes in universal preschool and if he’s elected president he’ll pump “billions of dollars into early childhood education.” Universal preschool is now second only to universal health care on the liberal policy wish list. Democratic governors across the country — including in Illinois, Arizona, Massachusetts and Virginia — have made a major push to fund universal preschool in their states. But is strapping a backpack on all 4-year-olds and sending them to preschool good for them? Not according to available evidence. “Advocates and supporters of universal preschool often use existing research for purely political purposes,” says James Heckman, a University of Chicago Noble laureate in economics whose work Mr. Obama and preschool activists routinely cite. “But the solid evidence for the effectiveness of early interventions is limited to those conducted on disadvantaged populations.” Mr. Obama asserted in the Las Vegas debate on Jan. 15 that every dollar spent on preschool will produce a 10-fold return by improving academic performance, which will supposedly lower juvenile delinquency and welfare use — and raise wages and tax contributions. Such claims are wildly exaggerated at best. In the last half-century, U.S. preschool attendance has gone up to nearly 70% from 16%. But fourth-grade reading, science, and math scores on the National Assessment of Educational Progress (NAEP) — the nation’s report card — have remained virtually stagnant since the early 1970s. Preschool activists at the Pew Charitable Trust and Pre-K Now — two major organizations pushing universal preschool — refuse to take this evidence seriously. The private preschool market, they insist, is just glorified day care. Not so with quality, government-funded preschools with credentialed teachers and standardized curriculum. But the results from Oklahoma and Georgia — both of which implemented universal preschool a decade or more ago — paint an equally dismal picture. A 2006 analysis by Education Week found that Oklahoma and Georgia were among the 10 states that had made the least progress on NAEP. Oklahoma, in fact, lost ground after it embraced universal preschool: In 1992 its fourth and eighth graders tested one point above the national average in math. Now they are several points below. Ditto for reading. Georgia’s universal preschool program has made virtually no difference to its fourth-grade reading scores. And a study of Tennessee’s preschool program released just this week by the nonpartisan Strategic Research Group found no statistical difference in the performance of preschool versus nonpreschool kids on any subject after the first grade. What about Head Start, the 40-year-old, federal preschool program for low-income kids? Studies by the Department of Health and Human Services have repeatedly found that although Head Start kids post initial gains on IQ and other cognitive measures, in later years they become indistinguishable from non-Head Start kids. Why don’t preschool gains stick? Possibly because the K-12 system is too dysfunctional to maintain them. More likely, because early education in general is not so crucial to the long-term intellectual growth of children.