Your review claims that the Perry study and the Abecedarian study are the sole evidence that preschool works. But they are just the best known of a large number of studies finding that preschool works, that is, has its intended effects on children. Along with the city-wide Chicago Child-Parent Centers study, these studies go a big step further by finding strong long-term effects and return on investment.
Please visit National Institute for Early Education Research (NIEER) for the complete blog post.