My just-published book, From Preschool to Prosperity, includes a chapter discussing common criticisms of the research evidence for early childhood programs. One frequent criticism of the evidence for early childhood programs is based on results from the recent Head Start experiment. These results show that most test score effects for the Head Start treatment group, compared to the control group, have faded to statistical insignificance by the end of 3rd grade. Critics see this evidence from a random assignment experiment, the “gold standard” of research rigor, as suggesting that early childhood programs do not work today, at least as currently designed and run on a large scale.
But test score fading is common for many early childhood programs. It is often the case that early test score effects, at the end of preschool or the beginning of kindergarten, have faded quite a bit by 3rd grade. But in many of these cases, the program still has large effects on adult outcomes.
For example, for the Perry Preschool program, the end-of-program effects on test scores are large enough to predict that the program would increase adult earnings by 12%. But the 3rd grade test score effects of Perry would only predict adult earnings increases of 2 to 5%. The actual adult earnings impact of Perry is estimated to be 19%.
Similar fading of test score effects, but recovery of effects on adult outcomes, is found for the Chicago Child-Parent Center program, and the Abecedarian program. For all three of these programs (Perry, CPC, Abecedarian), the end of the program test score effects were a better predictor of adult earnings outcomes than the 3rd grade test scores.
What is going on here? The most plausible explanation is that adult earnings outcomes are affected by more than what is measured by standardized test scores, which mostly measure cognitive skills. But social skills and character skills also matter. It is these harder-to-measure skill effects that persist and contribute to important adult effects on educational attainment and earnings.
Cognitive effects of preschool matter. But they matter as part of a process at which higher cognitive skills at kindergarten entrance, along with social and character skills, lead to more learning in kindergarten, and so on in first grade and at later ages. Educational achievement and attainment, and adult success in the labor market, can go up by a lot even if long-run IQ test scores don’t change much. The initial cognitive skill effects of preschool are useful to monitor as a signal of broader effects of preschool on both cognitive and non-cognitive skills.
We certainly know from conversations with employers that when employers complain about worker skills, they are not just referring to cognitive skills, but also to social and character skills. A big part of worker skills is showing up consistently on time. Another big part of worker skills is getting along with supervisors, co-workers, and customers.
Just as there’s more to life than test scores, there’s more to preschool’s benefits than is captured by long-run cognitive test scores.