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Preschool Longitudinal Studies


To many commentators, the best way to sum up the education crisis is to look at literacy. If a child hasn’t yet learned to read by third or fourth grade, the narrative goes, then they’ll be so far behind the other students that it’s very unlikely they’ll graduate from high school, go to college or succeed in the economy. And in fact, a large portion of children—especially those from low-income backgrounds—fit this narrative. But if you ask first grade teachers why their students aren’t learning to read, they throw up their hands. They say they’re doing all they can, but some children are simply more prepared than others. And so the debate often finds itself focusing on the preschool years: why do some students enter first grade with large vocabularies, strong work ethics, and advanced social skills, while others do not?

Research in early childhood development has shown that in addition to passing on their genes, parents pass on their cultural values and habits to their children. Infants who receive a lot of personal interaction, who are asked questions, read to, and given the resources to play, develop stronger cognitive skills and wind up doing better academically once they start school. Understandably, low-income parents are less likely to have the time, money or experience to provide these resources to their children.

Increasingly over the last several decades, policymakers have looked to preschools to bridge this gap. Underpinning their efforts are a series of long-term studies of the effectiveness of preschools, the two most famous of which are the Perry Preschool from Ypsilanti, Michigan, and the Carolina Abecedarian Project. Both studies are rigorous long-term evaluations of particularly successful early education programs.

The Perry Preschool was started in 1962 as a program of the Ypsilanti Public Schools. The preschool was started by David Weikart, who was the district’s special education director. According to Lawrence Schweinhart, who would eventually participate in the program’s evaluation:

The district’s ineffective way of coping with rampant school failure was grade retention. Weikart began the preschool program in an effort to get ahead of the problem. Many students had moved to Ypsilanti from a part of the country where some poor and minority students were not beginning their education until after first grade. Weikart and his colleagues reasoned that just as it would have been better for these students to have begun school in kindergarten as their classmates did, so it would have been even better for them to have started school a year or two earlier than that. (Schweinhart 2002)

Preschools were rare at the time, but the federal Head Start program was to start a couple years later, and researchers looking to learn more about preschool effectiveness went to Ypsilanti to study the program there. The first evaluation took place when graduates of the preschool were ten years old and found that they were only half as likely as other students to be held back a grade. This success convinced researchers to do another evaluation when the preschool graduates were 14 years old. As Schweinhart describes it:

When I first joined the research team, I was dubious about finding any longer-term program effects. After all, such long-term effects had never been found for a part-day preschool program. I had learned to be skeptical about research claims until all the evidence was in. The evidence did come in. I still remember my first look at the computer printouts revealing the substantial program effect on achievement test scores for 14-year-olds. I thought it was a mistake. Surely the weak effects found for first through fifth grades would disappear nine years after the kids had left the preschool program. But the effect was actually bigger than it was for the children in their earlier years, and it definitely was statistically significant. (Schweinhart 2002)

The positive findings convinced the researchers to do another study at age 19, then another at 27, and still another at 40. Every time, they found that participants in the program were less likely to be arrested, less likely to become single parents, less likely to depend on welfare, earned more money, and were more likely to own their own homes. 71% of participants earned a high school diploma or equivalent, compared to 54% of non-participants (Schweinhart 2002).

These findings are commonly expressed as a cost-benefit analysis. Researchers added up the costs saved to the criminal justice system and the welfare system, as well as the added revenue from more taxes collected from higher earners, and weighed them against the cost of the program in the beginning. They found that the Perry preschool actually saved the government money in the long run. The Perry program was actually a good financial investment, with a rate of return of about 7-10% per year. Expressing the findings in this way galvanized support for preschool education from the business community. (Schweinhart 2002)

The Abecedarian Project was a controlled experiment organized by the University of North Carolina at Chapel Hill in the late 1970s. Like the Perry program, it provided preschool education to children from a low-income background and compared their performance to a randomly-selected control group that were not provided with preschool. Also like the Perry program, the Abecedarian project emphasized emotional and cognitive development, and parents were involved in the program to a very high degree. Unlike the Perry program, though, they also provided some participants with specialized elementary school education until age eight, to learn more about how students adapted to a regular school environment (

The Abecedarian program primarily measured the cognitive skills of participants, unlike the Perry program which also measured social and economic indicators. So far, the Abecedarian graduates have been evaluated through age 30, and they have consistently outperformed the control group.

The Perry and Abecedarian programs are the most successful evaluations of preschool education to date. However, there have also been numerous studies of preschools which have not been so optimistic. Many preschools have been found to have no influence on student performance at all, and many others have found that the cognitive advantage of preschool disappears after a few years in regular elementary schools. The debate over preschool has become one of the main battlefields in the larger issue of education reform, and in the even larger question of the government’s role in reducing poverty.

Some conservative commentators, such as Charles Murray of the American Enterprise Institute, have questioned the validity of the studies’ findings. Murray argues that the sample sizes were too small, the randomization of the control group was not rigorous enough, and the evaluators were biased in favor of the programs. He points to other lackluster preschool evaluations as the norm, arguing that preschools are pretty much always ineffective.

However, most scholars accept the Perry and Abecedarian results as generally valid. More moderate critics remain concerned, though, about the exceptional nature of the findings. Why did these two programs do so well, when Head Start and other preschools have not? For example, Russ Whitehurst at the Brookings Institute points out that Perry and Abecedarian were very high-quality interventions. They were expensive: they provided several years of classes, they worked intimately with parents, they were staffed by highly-trained professionals and had the resources to buy quality materials and facilities. The Perry and Abecedarian programs spent approximately twice as much as Head Start spends per student. Whitehurst argues that these programs’ striking results have not been replicated on a larger scale because it’s simply too costly to invest in such expensive inputs.

This is understandable. After all, the goal of preschool is to provide children with the sort of intellectual and emotional stimulation they would not otherwise receive. Anecdotal accounts of “bad” preschools describe untrained caretakers who place children in front of the TV all day—it’s unsurprising that such programs don’t produce results. And if the elementary schools aren’t any better, then it would be expected that even a good preschool’s advantages would disappear after a few years.

Many scholars are still optimistic about preschool as a broadly useful tool to reduce poverty, however. Nobel-prize winning economist James Heckman of the University of Chicago is one of the leading advocates, defending the Perry and Abecedarian evaluation methods and arguing that educators are learning to recreate these results in lower-cost settings.

Questions for Reflections and Discussion

  1. In his 2013 State of the Union address, President Barack Obama advocated a universal preschool program, alluding to the results from Perry and Abecedarian. If you were in Congress, what would lead you to vote for or against such an initiative?
  2. Do you think we as a society should invest in a universal preschool as high-quality as the Perry and Abecedarian programs? Why or why not?
  3. Are you optimistic about the development of lower-cost, effective preschools? Why or why not?


  1. The Perry and Abecedarian preschool programs achieved impressive results, showing that a careful and well-funded preschool can dramatically change the socioeconomic disadvantages of participants.
  2. It remains questionable whether a lower-cost preschool can achieve the same results, or whether it is reasonable to expect a universal highly-funded program.
  3. A rigorous scholarly evaluation of a social program can be phenomenally persuasive to convince policymakers to invest in the idea, though there will always be critics who question the findings.

Peter Bass
© 2018 CYS

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