The Perry Preschool study is famous among social policy researchers. In the early 1960s, a sample of low-income African-American children who were assessed to be at high risk of school failure were randomly assigned to two groups, one of which received two years of high-quality preschool and one of which did not receive a preschool program. The group that received preschool services scored higher on IQ and similar tests while in preschool and for a year or two afterward, but this achievement gap faded over time. However, the group that received preschool services continued to score higher on school achievement tests and be more likely to complete school, more likely to be employed, and less likely to be arrested, even decades later.
The full report of the 40-year followup doesn't seem to be available yet, but a summary report including Q and As is available on the web. It's a fascinating read, and makes some interesting points.
- Almost all of the impact on high school graduation is driven by the women. 84 percent of the women in the preschool group graduated from a regular high school compared to 32 percent of the non-program group. (This is an impact so large as to be almost inconceivable -- social service interventions typically move impacts by a few percentage points.) The researchers suggest as a possible explanation that boys were more likely to be held back or assigned to special education because of behavioral issues, not just academic delays.
- Almost all of the cost savings, however, are driven by the reduction in arrest and incarceration, which is concentrated among the men. The researchers estimate that each dollar invested in the Perry Preschool program returned over $17 -- almost $13 for society as a whole, and $4 for the participants. Of the return to society, 88% came from the reduction in crime.
- This study was one of the driving forces behind the creation of the Head Start program, and is still cited as one of the main pieces of evidence in support of the program. However, the researchers note that most Head Start programs are not as good as the studied program -- especially in regard to the educational background of the teachers.
- The researchers also caution against using this study to argue for universal preschool. They say that this study shows that "educational productivity in early childhood settings has a large influence on young children's subsequent lives." The Perry Preschool was dramatically more "educationally productive" than the homes and neighborhoods in which these poor kids would have spend their days otherwise. But the researchers argue that neither home nor preschool settings are inherently more educationally productive. So, while these children benefited greatly, "young children from educationally productive homes who attend less educationally productive early childhood programs would suffer negative effects on their development."