Perry and Abecedarian Projects FAQ

The Perry Preschool Project and The Carolina Abecedarian Project are two widely acclaimed early childhood education intervention programs that have followed participants for over half a century, reporting promising results along the way. Critics, however, have grown skeptical about the accuracy and relevance of these programs, especially as these programs have increasingly been used to justify larger-scale early childhood efforts. Below are responses to common concerns.

"The sample sizes in Perry and Abecedarian were too small for results to be conclusive."

We can have confidence in the Perry and Abecedarian results even if the studies had relatively small sample sizes because this limitation is taken into account within the measure of statistical significance. Results from Perry and Abecedarian are so strong that they survive conservative statistical procedures that account for small sample inference. Furthermore, when using a 5% significance level, one would expect that 5 out of 100 hypotheses would be “significant” just by chance. Heckman’s widely accepted analysis of Perry outcomes shows that significant differences between treated and untreated children remain even after accounting for the possibility that some outcomes may appear significant due to chance alone.


“The positive effects on IQ scores initially seen in Perry and Abecedarian disappeared over time.”

It is true that both Perry and Abecedarian did not show any positive IQ effects just a few years following the intervention program. Decades of follow-ups, however, have shown extremely encouraging results along dimensions such as schooling, earnings, crime involvement, and health. Professor Heckman and colleagues believe that we may be focusing on the wrong set of traits, as the “soft stills” gained by students who have attended these programs—conscientiousness, self-control, motivation, etc.— tend to be much more predictive of success in adulthood. It is these skills that facilitate the better performance of treatment students on achievement tests despite performing no better on IQ tests. Another possible explanation for the “fade-out” in IQ, offered by Perry researchers, is that these results many have more to do with the way in which we test for improvement than the amount of improvement itself.


“Perry and Abecedarian were high quality programs. Thus, findings from these programs cannot be generalized to large-scale attempts at offering pre-kindergarten.”

There is no doubt that the quality of the program is of supreme importance to its success. The Perry Preschool Project, for example, hired teachers with bachelor’s degrees and certification in education, kept class sizes below 8 students, and included weekly teacher home visits. That said, Heckman and colleagues are confident that state, federal and private early childhood education programs that model programs like Perry can deliver a 7-10% annual return on investment, which is comparable to the post World War II return on equity in the US stock. This projected return serves as a strong economic incentive to have high standards for large-scale programs as well.


"Head Start has failed to replicate the results seen in Perry and Abecedarian. According to the Head Start Impact Study (HSIS), the first randomized controlled trial of the program, all positive effects faded by 3rd grade.”

While results have been disheartening, HSIS has a host of limitations that must be considered. To begin with, it compares apples to apples: Over 60% of control children either attended alternate preschool programs or were accepted into Head Start through a later lottery while 18% of students in the treatment group chose not to attend Head Start at all. These factors dilute any gains achieved by Head Start. Another limitation is that the study cannot control for the different amounts of attention children receive when they enter elementary school. Since control children were behind at the end of the program, it is possible that teachers worked to catch them up. But even in the highly unlikely case that these factors do not affect reported results, it is still possible that we will observe positive effects emerge at later years. The truly remarkable impacts of Perry and Abecedarian were not seen until much later in the lives of participants. Also, while HSIS is in its early stages, there are numerous long-term, quasi-experimental studies that find Head Start children to attend more years of schooling, earn higher incomes, live healthier, and engage less in criminal behavior. Considering this, it is especially important that we see HSIS through before condemning Head Start.