On June 26 USA Today reported on the findings of a preschool study which concludes that Oklahoma’s government-run preschool gives a boost to the performance of all students in the short-term. This is news because the collective conclusions of previous studies overwhelmingly suggest that preschool boosts at-risk children in the short-term, but not children from middle- and upper-income families.

“An ambitious public pre-kindergarten program in Oklahoma boosts kids’ skills dramatically, a long-awaited study finds, for the first time offering across-the-board evidence that universal preschool, open to all children, benefits both low-income and middle-class kids,” Greg Toppo reported. “More than any other state, Oklahoma has pushed for universal pre-kindergarten, with the USA’s highest enrollment rate.”

There’s just one tiny problem. Oklahoma’s achievement scores on National Assessment of Educational Progress (NAEP, also known as “the nation’s report-card”) suggest that the state’s universal preschool program is at best ineffective and at worst harmful to student achievement.

Oklahoma, “where state-funded pre-kindergarten has been in place for 18 years—and offered universally for nearly a decade,” has slipped below the national average on math and reading scores for both the 4th and 8th grades since it began expanding government pre-K in the 1990s.

Oklahoma slipped from one point above the national average in 4th grade math in 1992 to two points behind in 2007. They slipped further behind in 8th grade math, from one point ahead to five points behind the national average.

In reading, the story’s the same; 8th grade scores slipped from four points ahead in 1998 to one point behind. And Oklahoma’s 4th grade reading scores plummeted during the 1990s at the very same time the state was aggressively expanding preschool access, increasing attendance, and building a system that the National Institute for Early Education Research (NIEER) rates 9 out of 10 on quality.

There is little evidence in the research that these kinds of preschool programs impart lasting gains to low-income students and no evidence that they benefit middle-class kids. The real-world evidence demonstrates that the test scores of children in Oklahoma have eroded significantly, as have our nation’s performance on international tests, at the same time that preschool programs have massively expanded and the quality of those programs has supposedly improved.

Adam Schaeffer (Ph.D., University of Virginia) is a policy analyst at the Cato Institute.