“Startling Insights From a New Preschool Study” blares the headline from a SciTechDaily article on a new review of early childhood education research. The article is attributed to the Teachers College at Columbia University, home of two of the study’s authors.

But is this really startling given that most studies show mixed results at best?

The new report, “Unsettled science on longer-run effects of early education,” notes that most of the positive enthusiasm for taxpayer support of preschool comes from two projects in the 1960s and 1970s. The Abecedarian Preschool Study and the Perry Preschool Project each enrolled fewer than 60 children, included family support beyond the preschool programs, and were costly. It’s not surprising they have never been replicated on a large scale.

Given the impracticality of duplicating these tiny programs, it’s rather absurd that, as the “Unsettled science” report puts it, “The rigorous and notably positive evidence from these two studies all but ended the debate over the longer-run effectiveness of early childhood education programs.” Yet when it comes to broader preschool programs, these benefits are largely absent.

Head Start, run by the US Department of Health and Human Services (HHS), is the largest preschool program in the United States. In 2012, HHS released the results of the most comprehensive study of the program, finding little or no effect on student outcomes that persisted through third grade. Troublingly, as the “Unsettled science” report notes, there was even evidence that children who participated in Head Start “displayed more emotional symptoms than children who lost the lottery.”

These poor results were despite the program costing more than $7 billion per year at the time ($7,900 per child). It now costs around $12 billion, or more than $14,000 per child. But there is still no evidence of persistent benefits from the program.

The report also references a 2022 study of Tennessee’s Voluntary Pre‑K program. I recently had the opportunity to testify at a Congressional Joint Economic Committee hearing on “Building Blocks for Success: Investing in Early Childhood Education.” In my testimony, I noted,

There’s no consistent evidence that large-scale preschool programs are beneficial; and there’s evidence they can even be harmful. In January 2022, researchers from Vanderbilt University released a randomized study of Tennessee’s Voluntary Pre‑K initiative that found that children who participated in the program experienced “significantly negative effects” compared with the children who did not. Harms included worse academic performance and higher likelihood to have discipline issues and be referred for special education services. The results were so shocking that the researchers had to “go back and do robustness checks every which way from Sunday,” according to Dale Farran, one of the lead researchers. “At least for poor children, it turns out that something is not better than nothing,” she said.

The only positive outcomes in the “Unsettled science” report were in Boston, where there was a recent lottery-based evaluation of cohorts entering the city’s public pre‑k program between 1997 and 2003. Researchers found positive impacts on high school graduation and college enrollment, as well as fewer disciplinary problems in high school. But neither this nor a separate study of Boston’s program showed any positive impacts before high school.

The new study acknowledges, “the Boston evaluation leaves unanswered many important questions: In particular, what went on in the classrooms, and how can we explain the program’s longer-run impacts, given that there were no detectable achievement and behavioral impacts across the first eight grades of school?”

The inconsistent and sometimes negative results from large-scale preschool programs point to an important fact when it comes to any educational endeavors: one size does not fit all. A program that works for some children may be terrible for others. That’s why it’s crucial that the federal government, especially, stays out of early childhood education.

The first sentence of the “Unsettled science” report claims, “Early education programs are widely believed to be effective public investments for helping children succeed in school and for reducing income and race-based achievement gaps.” If it’s “widely believed” that large-scale preschool programs are an effective tool, that’s because people want it to be so, not because the evidence backs up that belief.