In Ypsilanti, Michigan, 3 and 4 year-olds from low-income families were randomly assigned to participate in the Perry Preschool. By age 18, they were five times less likely to have become chronic law-breakers than those who were not selected to participate in the Preschool.
The Perry Preschool Study also found that low-income individuals who were enrolled in a quality preschool program earned on average, by age 40, $5500 per year more than those who were not. The Perry Preschool Study produced a total benefit/cost ratio of 17:1 (4:1 for participants, 13:1 for the public), with participants on average earning higher incomes, more likely to own their own homes, and less likely to be on welfare.
The authors of the Perry Preschool Project also propose that the return on investment in education declines with the student's age. This study is noteworthy because it advocates for public spending on early childhood programs as an economic investment in a society's future, rather than in the interest of social justice.
In 2008, Michael L. Anderson re-examined the data from Perry and similar projects and found "... girls garnered substantial short- and long-term benefits from the interventions. However, there were no significant long-term benefits for boys."
Source: The Perry Preschool Project