California has fallen behind on many key indicators of education performance, prompting policymakers to look for strategies to improve student outcomes. Among the policy options being considered is the possibility of expanding public funding for preschool education as part of a broader agenda of education reform. To provide a foundation for evaluating the potential of such an expansion and how best to implement it, the RAND Corporation is undertaking the California Preschool Study, which seeks a better understanding of: (1) the size of achievement shortfalls overall in the early elementary grades and gaps in school performance between groups-- defined, for example, by race-ethnicity or socioeconomic status--and the potential for preschool education to close existing gaps; (2) how publicly funded early care and education (ECE) programs are structured and how effectively ECE funds are being spent; and (3) rates of access to high-quality early learning programs among California's children. This research brief summarizes findings of the study of the use and quality of early care and education programs serving preschool-age children in California and the extent to which some groups of children are particularly underserved. (Contains 2 figures.)