Studies on lauded pre-kindergarten programs have shown impressive short-term benefits that sometimes last into adulthood. But are results similar for typical pre-K programs offered at school districts across the country?

An Upjohn Institute study, the first national look at the effects of public-school pre-K programs, finds much stronger impacts on fourth grade outcomes when the programs are of higher quality or are carried out in more disadvantaged school districts. The working paper is “Pre-K in the Public Schools: Evidence from Within U.S. States,” by Timothy Bartik and Brad Hershbein.

Majority African-American districts with pre-K programs have significant improvements in math and reading scores in fourth grade, the study found, and possibly need less special education and have fewer children behind grade level.

Programs in states that the authors determined to have high-quality programs also see benefits persisting to at least fourth grade, with significant boosts to math scores. Reading scores tend to increase as well, but the differences are not statistically significant.

In contrast, for the average student in the average school district and state, the typical pre-K program has no significant effects on fourth-grade test scores or other fourth grade outcomes.

Many studies, including those from the Upjohn Institute, have shown lasting benefits from pre-K programs, both in students’ school performance and in their adult careers. Policymakers have pointed to those programs’ successes as justification for getting more children into prekindergarten.

The most dramatic findings often come from research on small, expensive pre-K programs targeted at disadvantaged students. The programs they inspired, however, were bigger—sometimes open to every student in a state—often cheaper, and possibly of lower quality.

Bartik and Hershbein reasoned that results also might be less impressive for children with access to other resources, including private early education programs. They looked at the effectiveness of typical programs in public schools, using detailed district-level enrollment and performance data to measure the average effect of pre-K on later outcomes. Those outcomes included math and reading standardized test scores, the share of students receiving special education services, and the share of students older than the fourth-grade age cutoff (a proxy for being held back).

In majority African-American school districts, the typical pre-K program has significant benefits. A district shifting from no pre-K to full pre-K enrollment improves math scores by 6 percentiles and reading scores by 4 percentiles. In high-quality states, majority African-American districts see their scores increase by even larger amounts, roughly 7 percentiles in both math and reading.

High-quality states also see pre-K benefits for students overall, with increases in average math scores of almost 3 percentiles. These test score increases are large enough that such programs would be predicted to increase adult earnings sufficiently to justify pre-K’s costs.

But for the average student in the average school district and state, the average pre-K program has statistically and substantively insignificant effects. While even modest effects could produce enough benefits to society to justify the programs’ cost, the study’s results are precise enough to rule out any large returns in these cases.

This research, despite not finding positive effects on average, shows that large-scale pre-K programs can provide benefits if they are either well targeted or of high quality, and even more so if they are both. The results, Bartik and Hershbein note, also don’t rule out “sleeper effects”—that is, benefits that become apparent only later in life. Social skills taught in early education, such as teamwork, don’t show up on academic tests but serve students throughout their schooling and careers.

These results are relevant to current policy debates about expanding pre-K to a larger scale. Bartik and Hershbein’s findings suggest that states expanding pre-K need to keep these programs’ quality up.

Read the policy brief | read the working paper.