In 2014, New York City launched the historic Pre-K for All program, which massively expanded early education for children in the city. The state followed suit with a budgetary pledge of some $1.5 billion over 5 years to implement full-day universal prekindergarten (pre-K) statewide. Many other states have implemented or expanded state-funded pre-K programs in the last decade, encouraged by claims about expected benefits. However, there is remarkably little scientifically rigorous evidence for these benefits. Claims of pre-K success rely largely on small, experimental, model programs run 50 or more years ago--programs that bear little resemblance to current pre-K implementations. Evidence for program effectiveness is crucial given the current interest in and expansion of state-funded pre-K programs. This review of the evidence raises serious questions about the presumed benefits of state pre-K programs. (author abstract)