There is a new Best Evidence in Brief, and this time, I picked this study from this biweekly newsletter written by Susan Davis, Johns Hopkins University.

A study by Johnson and colleagues has been the first to examine if, among students from low SES backgrounds, benefits to public or Head Start preschool attendance the year prior to kindergarten were still evident in third grade.

The study involved  689 students from low-SES backgrounds in the Tulsa, Oklahoma public school district who were third graders in 2021. Researchers used propensity score weighting to balance the baseline characteristics of the children, enabling a comparison of third grade achievement data of students who attended public pre-K, Head Start pre-K, or no pre-K the year before kindergarten (2017-18). Results, using literacy and math subtests from the Woodcock-Johnson, showed that academic performance favored pre-K attenders, with the most pronounced differences observed in kindergarten. However, these advantages diminished by third grade, excepting numerical fluency among Head Start pre-K attenders, whose outcomes in numerical fluency had further increased by third grade. In  conclusion, both public school and Head Start pre-K programs benefitted students from low-income backgrounds into third grade, despite that the extent of the benefits as compared to pre-K non-attenders decreased over time for most areas.

This result doesn’t surprise me that much, as it is in line with previous research that often gave the same nuance to the Heckman curve:

That is why James Heckman changed his theory to the Heckman Equation, adding the important element of sustaining: