Parents and public officials are increasingly concerned about the school readiness of young children. In response, in recent years, state governments have boosted their support for pre-K programs. Several states, including Oklahoma, have opted for universal pre-K, making it available, on a voluntary basis, to all 4-year-olds. At the same time, the federal government, through the No Child Left Behind Act, has imposed new testing requirements on public schools to determine whether students as a whole and particular subgroups of students are making good academic progress. These trends have heightened interest in the effectiveness of pre-K programs.

The Oklahoma pre-K program is of special interest because it enrolls a higher percentage of 4-year-olds than any pre-K program in the United States (Barnett, Epstein, Friedman, Sansanelli, & Hustedt, 2009). It is also of particular interest because it is based in the public schools and because it places strong emphasis on high quality: All lead teachers must have a college degree and be early-childhood certified; to facilitate the recruitment and retention of outstanding individuals, lead teachers are paid at the same rate as other public school teachers.

Many studies have demonstrated that considerable benefits flow from a high-quality targeted pre-K program. But can a large-scale universal pre-K program also produce substantial benefits by enhancing the school readiness of young children? Do all children benefit from such a program? Do some children benefit more? And how large are the impacts of such a program, in absolute or relative terms?