A new paper by Elizabeth Cascio and Diane Whitmore Schanzenbach provides important new evidence on the effects of universal pre-K. This paper was presented in late September at the Brookings Panel on Economic Activity.

Cascio and Schanzenbach examine the effects of universal pre-K in Oklahoma and Georgia. The focus is on effects on overall pre-K enrollment (that is, total enrollment in both private and public pre-K programs), and on effects on 8^th grade test scores.

A possible concern about universal pre-K is that its availability may be mostly or entirely offset by reduced enrollment in private pre-K. If this “crowd-out” of private pre-K occurs, then this may reduce the net overall effect of universal pre-K on participants’ skills. For a participant who enrolls in public pre-K, but otherwise would enroll in private pre-K, the net effect of the universal pre-K program on skills may be reduced. Perhaps the private pre-K would have increased skills almost as much as the universal pre-K program, or by even more.

Although Cascio and Schanzenbach find some crowd-out, it is not close to being 100%. Universal pre-K significantly increases overall pre-K enrollment.  This enrollment increase due to universal pre-K occurs for both disadvantaged students, and advantaged students.  The crowd-out effect is somewhat larger for advantaged families, but there is still a sizable net increase in enrollment for this group.

Cascio and Schanzenbach also find that universal pre-K increases 8^th grade test scores for disadvantaged students, compared to what would have occurred in states without universal pre-K. For more advantaged students, they do not find statistically significant effects of universal pre-K on 8^th grade test scores.

Some media reports have spun these results as showing that universal pre-K does not provide long-term benefits to middle-income children.  A more balanced interpretation is that the Cascio and Schanzenbach results do not provide strong evidence either for or against many of the most important potential long-term effects of pre-K programs for the middle-class.  A particularly important long-term economic effect of pre-K is effects on former participants’ adult earnings. 8^th grade test score effects are unlikely to be strongly predictive of whether or not there will be future adult earnings effects.

Several good studies suggest that 8^th grade test score effects are not a good indicator of whether an early intervention affects adult earnings. Chetty et al. find that kindergarten “class quality” has effects on test scores that fade, but that effects of kindergarten class quality on adult earnings are still significant.  (The Chetty et al. paper is “How Does Your Kindergarten Classroom Affect Your Earnings?”, and can be found on this page.) Chetty et al’s results find that effects of kindergarten class quality on kindergarten test scores can be used to predict reasonably accurately the eventual effect of kindergarten class quality on adult earnings.  But kindergarten class quality’s effects on 8^th grade test scores are so small that they predict effects on adult earnings that are less than one-sixth of the adult earnings effects that we eventually observe.

Deming finds that Head Start has sizable effects on adult earnings, even though effects on test scores fade to statistical and substantive insignificance by 8^th grade. Head Start’s initial test score effects decrease by over 60% by ages 11-14, and are no longer statistically significant. Despite this fading of test score effects, Deming finds significant Head Start effects on adult outcomes that are sufficient to predict that Head Start increases adult wages by 11%.

What might explain this fading and re-emergence of the effects of early intervention? One possible interpretation is that many early interventions significantly increase both “hard skills” (academic skills) and “soft skills” (social and character skills) in the short-run. Some of the hard skill effects fade over time, but the soft skill effects continue, and lead to better adult outcomes.  Soft skills are hard to directly measure, and so most school test scores really measure hard skills. The initial hard skill effects on early test scores of early interventions may indicate an increase in both hard skills and soft skills due to a well-run program, and may be a better predictor of long-run adult earnings effects than the faded hard skill effects that are observable in later grades.

In sum, I don’t think that Cascio and Schanzenbach’s new research is inconsistent with the previous research literature on universal pre-K. This previous research has found that universal pre-K has strong effects on early test scores for both low-income and middle-class students.  My paper with Gormley and Adelstein on Tulsa’s universal pre-K program found that this program had similar early test score effects for both low-income and middle-class students. We used these early test score effects, and the links developed by Chetty et al. between early test scores and adult earnings, to project that Tulsa’s program would have similar dollar effects on increasing adult earnings for both low-income groups and middle-class groups.  Weiland and Yoshikawa’s recent study of Boston’s universal pre-K program also finds similar effects on early test scores for both low-income and middle-class children. In a recent blog post, I used their results to project that Boston’s program is likely to have similar dollar effects on adult earnings for both low-income groups and the middle-class.  Cascio and Schanzenbach’s new research does not provide strong evidence for or against these projections that universal pre-K will have similar effects on adult earnings for both the poor and the middle class.

Cascio and Schanzenbach’s study points out that one good rationale for universal pre-K is the possibility of significant peer effects. If having more middle-class children in a pre-K classroom tends to provide positive peer effects that enhance the learning of low-income children, then part of having quality pre-K for the disadvantaged is having income-integrated pre-K classrooms.  Income-integrated classrooms are much easier to implement under a universal pre-K system than under an income-targeted pre-K system.

The weight of the research evidence continues to suggest that universal pre-K has broad benefits for many income groups.  This research evidence, along with the potential broader political support for universal pre-K, are good reasons to support making expanded pre-K accessible to as many families as possible.