Defying conventional wisdom, a statewide study on Tennessee’s voluntary state preschool program shows children who participated in the program didn’t perform any better than children who didn’t attend pre-K.

The study is the first large randomized control test of a state funded pre-K program.

Vanderbilt Institute Research Professors Mark Lipsey, Dale Farran, and Kelley Durkin conducted a randomized control test on 3,131 eligible children who applied for admission at one of 79 oversubscribed VPK programs in Tennessee.

Although the study found positive short-term achievement by the end of pre-K, those gains disappeared as VPK children entered elementary school and even turned negative by the third grade. The control group scored higher in math and science than the group who attended the pre-K program.

In math, the VPK group saw roughly 13 percent less growth in math achievement than expected. In science, the VPK group saw around 23 percent less growth.

Researchers found no significant impact on reading achievement in the third grade, or on school attendance, grade retention, or disciplinary infractions from between pre-K to third grade.

What researchers found is VPK participants were designated as needing special education services at a slightly higher rate than the control group. This is one possible explanation for the outcomes of the study, as the researchers conclude that “such identification may then lead to lower educational expectations and levels of instruction for these children.”

The researchers said another explanation is some children may be better off academically if they stay at home instead of attending pre-K.

Terry Stoops, vice president of research and director of education studies at the John Locke Foundation, said unlike most studies on state pre-K programs, the Vanderbilt researchers used a randomized control test, the “gold standard” in social science research.

“By randomly assigning students to control and treatment groups, the researchers minimized the possibility that the results were due to unobserved characteristics of each group,” Stoops said.

The Tennessee study doesn’t necessarily spell trouble for North Carolina’s pre-k program. Rob Thompson, deputy director of the advocacy group NC Child, said people shouldn’t draw conclusions from a Tennessee study about how North Carolina’s program is working.

“We do a pretty rigorous job studying what we do in North Carolina through the Frank Porter Graham Institute and we conduct annual evaluations of the program and the results for participants,” Thompson said. “Year after year we get really positive results.”

A February 2017 study from the Frank Porter Graham Institute found by the end of kindergarten, pre-K participants scored significantly higher on math, but saw little difference in literacy and language skills. A May 2017 study of North Carolina’s pre-K program from the same researchers showed positive improvements in math, literacy, and language skills of children who attended the state program.

But the studies didn’t use a randomized control test and compare outcomes of children identified sometime after they did or didn’t attend pre-K, which the Vanderbilt researchers argue could lead to selection bias.

“In short, why did some parents take advantage of a voluntary pre-k program while others did not, and how is that related to family and child characteristics that might influence later outcomes?” the Vanderbilt researchers asked.

The N.C. Pre-K program has served more than 350,000 children since it started in 2001. Democrats and Republicans alike have indicated a desire to expand the program to serve more children and clear up any waiting lists.

“Preschool, when it is well designed and well implemented can play a really critical role in helping the development of kids’ brains,” Thompson said.

Thompson said the Tennessee study points out that the classrooms the researchers looked at were all different, which accounts for some of the outcomes they saw.

“It is really important we have a high-quality N.C. pre-k program because all child care and all preschool isn’t the same,” Thompson said.

Earlier this year, lawmakers agreed to spend more than $80 million for the 2019-20 fiscal year and more than $90 million for the 2020-21 fiscal year to expand the state’s pre-k program.

“I still think there is a compelling case for targeted preschool programs, such as those for poor and neglected children, but the results of this study undercut the case for expansive, state-funded early education programs,” Stoops said.