Tom Daula writes:
Apparently there are two papers on a long-term study of Tennessee’s preschool program. In case you had an independent interest in the topic, a summary of the most recent paper is here, and the paywalled paper is here.
The research paper, by Mark Lipsey, Dale Farran, and Kelley Durkin, concludes:
This study of the Tennessee Voluntary Pre-K Program (VPK) is the first randomized control trial of a state pre-k program.
Positive achievement effects at the end of pre-k reversed and began favoring the control children by 2nd and 3rd grade. . .
It’s a long paper and I have not read it in detail so I won’t attempt to evaluate this empirical claim. At first it might sound surprising that preschool did not show positive effects, but the authors in section 6 of their paper do give some reasons why this might be the case.