I found the comments on the talk of interest. Many of these comments reflect common misunderstandings of the research evidence for pre-K’s benefits. I responded to some of these comments at the TED website, but let me summarize some of the key points here.
1. We have good evidence that pre-K actually causes better outcomes for former participants, because many research studies have good comparison groups. Several commenters argued that better parents will send their kids with preschool, therefore evidence that kids with preschool do better in later life does not mean that preschool caused these differences.
But the research evidence on the benefits of pre-K does not rely on simple comparisons of kids with pre-K vs. kids without pre-K. Rather, this research relies on studies in which the treatment and comparison group are quite similar except for access to pre-K.
This research evidence includes studies (Perry, Abecedarian) that use random assignment to determine access to pre-K, which means on average we would expect both the treatment and control groups to be similar in all pre-existing observed and unobserved characteristics. Some studies compare children in similar neighborhoods with different access to pre-K (e.g., Chicago Child-Parent Center study). Some studies compare siblings, one of whom attended pre-K, and the other who did not attend pre-K (e.g., Deming and Currie et al. studies of Head Start). Some studies compare counties with similar poverty rates that had different access to pre-K because of federal funding policies (Ludwig and Miller). Some studies compare students who just missed the age-cutoff for pre-K the previous year, and are just starting pre-K, with similar aged students who just made the age cutoff the previous year, and therefore have completed pre-K and are starting kindergarten (e.g., many state pre-K studies, of West Virginia, Michigan, Oklahoma, New Jersey, South Carolina, New Mexico, Arkansas, and Tennessee, and studies of Tulsa and Boston).
Because all of these studies are comparing similar children, the short-term and long-term benefits found for children who attended pre-K are plausibly attributable to pre-K, not pre-existing differences. We know more about whether pre-K works than about whether 3rd grade works. For 3rd grade, we have universal access. It would be unethical to flip a coin and deny some child access to 3rd grade in order to facilitate a research project. In contrast, for pre-K, we have natural and planned experiments in which access to pre-K services has varied for otherwise similar children.
2. The evidence for the long-term benefits of pre-K for middle-class children is more indirect than the evidence for low-income children, but the most consistent interpretation of the research data is that education-oriented pre-K programs have broad benefits for children from many income groups. Several commenters argued that the main long-term studies of pre-K, such as Perry, Abecedarian, and Chicago CPC, are for programs that serve disadvantaged children, and therefore these studies do not provide direct evidence for long-term benefits of pre-K for middle class children.
However, we have good evidence for the short-term benefits of pre-K for middle class children, for example from Tulsa and Boston. These short-term test score gains are similar for middle-class and low-income children. There also is one random assignment study of middle-class children that shows some evidence of test score gains. State pre-K studies include states with universal (Oklahoma) or relatively broad criteria for pre-K eligibility (Michigan, West Virginia), and such states do not seem to show significantly lower short-term test score effects of pre-K than states with more targeted programs.
Furthermore, research by Chetty et al. suggests short-term test score gains will have true causal effects in increasing adult earnings. Combining these two lines of research (pre-K yields similar test score effects for low-income and middle class children, test score gains in kindergarten lead to higher adult earnings), a reasonable inference is that pre-K will produce adult earnings gain for middle class children.
Middle class and upper class families certainly seem to believe that preschool will help their children, as pre-K enrollment rates for families in the top quarter of the income distribution tend to be 10 to 20 percentage points higher than for families in the bottom half of the income distribution (Duncan and Magnuson, 2013).
If pre-K’s effects are in part due to effects on social skills or soft skills of getting along with peers and teachers and other authority figures, then it is reasonable to expect pre-K to have benefits for middle-class children. Skills of getting along with peers and outside authority figures are hard to develop without the experience of a formal group setting.
It would be nice if we had random assignment evidence of the long-term effects of preschool for middle class children. But given that such a study has not been done, and is unlikely to ever be funded, policymakers must make decisions on the weight of the available empirical evidence. This evidence suggests that preschool has broad benefits that include many middle class children.
Finally, it should be recognized that according to the Current Population Survey, a little less than one-quarter of all U.S. children under the age of five are in families below the poverty line, and a little under one-half of all U.S. children under the age of five are in families below 200% of the poverty line. Therefore, even a pre-K program that “targeted” poor and near-poor children would have to serve close to half of all four-year-olds.
3. Pre-K probably has positive spillover benefits that exceed its individual benefits. One commenter argued that the individual benefits for pre-K does not mean it has a collective benefit, as part of the individual benefits may occur due to some kids getting a “kick start” to do better than the other kids in their class in the competition for being recognized as a good student and thus developing self-confidence.
But this ignores possible positive spillovers. If more kids have higher academic skills because of preschool, this will allow kindergarten and later teachers to teach at a higher level, which will increase student learning. In addition, this will mean fewer kids in remedial education programs, which means more time and other resources for the remaining kids in remedial programs. If pre-K leads to better social skills, then there will be fewer disruptions in the K-12 system due to behavioral problems, and fewer classroom disruptions mean that all students learn more. Students may learn from other students in their class, so if pre-K increases student achievement levels, this increases the potential for more learning from peers.
The empirical evidence does suggest that there are positive peer effects of having students in your classroom with higher educational achievement. Therefore, the empirical evidence suggests that the positive spillovers from more educated peers exceed any potential negative spillovers from the greater competition.
Finally, one of the key arguments of my TED talk is that there are positive spillovers in adulthood of individual skills, due to their effects on the competitiveness, profitability, and wages paid by employers. Even if I already have a college degree, the empirical evidence suggests that when more workers in my metro area have a college degree, the positive spillovers of their skills tend to increase my wages more than any negative effects on wages of having more labor market competitors. These positive spillovers include that with many workers with more skills, my employer and my employer’s suppliers will be more productive and better able to develop and introduce new technologies, which will increase the competitiveness of local businesses and thereby increase everyone’s wages.
In sum, there is strong research evidence for broad long-term benefits of pre-K for children from many income groups. The main point of my TED talk is that these effects on the skills of individuals will also translate into large local economic development benefits from state government investments in quality pre-K programs.