Although extensive research points to the potential payoffs from early childhood investments, much of the research is dated, has involved very small samples or has used less than rigorous research designs. As a result, there is a surprisingly thin body of evidence to guide specific decisions on how to design, target and implement public investments in preschools. Such investments have grown substantially over the last decade and more information is needed about how to ensure these investments pay off. This study will take place in two localities and will test whether an academic boost from a six-week school-readiness program in the summer right before kindergarten is a cost-effective way to improve outcomes (and prevent summer learning loss) for children who have been in preschool during the regular school year. The summer program will also be tested for children who were not in a preschool program during the regular academic year, to show whether the short-term intervention can help these children catch up to their peers who did attend preschool programs during the academic year. This project is part of a larger venture designed to provide new and useful information to policy makers and others investing in public preschool regarding the approaches that are likely to lead to the most effective preschool programs.