Relatively few rigorous studies of the effectiveness of contemporary public prekindergarten programs have been conducted despite the growing number of programs and large monetary investments they require. The study on which this presentation is based was launched in partnership with the Tennessee State Department of Education's Division of School Readiness and Early Learning to provide an assessment of the effects of the statewide Tennessee Voluntary Prekindergarten (TN-VPK) program on the readiness for kindergarten of the economically disadvantaged population it serves. Research studies have reported the rapid neurological, cognitive, and social-emotional growth that takes place during the first five years of life and the positive effects of high-quality early childhood educational programs. In recent years, however, TN-VPK has become a controversial program in Tennessee, with some legislators expressing doubts about its value in the context of severe budget shortfalls and still others referring to it even more skeptically as expensive babysitting. This study interleaves a longitudinal randomized control trial (RCT) and an age-cutoff regression discontinuity (RD) design to evaluate the effectiveness of the TN-VPK program. Though the project is still underway, this presentation will summarize results for two cohorts of RCT participants.