boots, did you even read about the study before commenting?   The study was done in a small town in Michigan.  All participants were African American and they all had a parent who was at home during the day.   It is very likely that the intense home intervention had more to do with the participants success than the preschool itself .     Modern studies of preschool show that preschool benefits are very minimal and any benefits of preschool typically disappear by third grade.