"Just funding preschool doesn't mean it's going to be effective," he adds. "You have to follow the principles of quality."
That means having qualified teachers and providing a structured but nurturing environment. In addition to the quality of the program itself, another reason the Chicago preschools may have had such a large impact is that they helped parents feel that they were part of a community and kept them involved with their children's school. This cut the number of parents who frequently moved their children from one school to another by half.