The emergence and transformation of kindergarten in the United States is the quintessential example of the irrepressibility of schooling expansion, the ever-greater institutionalization of education in children's lives, and the rise in formal education's emphasis on cognitive skills among young children. This article explores the cultural transformation of kindergarten from a separate play-based experience to the first year of formal schooling. This happened all while kindergarten enrollments expanded. Over the course of the twentieth century, parents increasingly opted to enroll their children in formal schooling prior to compulsory attendance requirements, regardless of mothers' work status. Instead, enrollment rates are associated with mothers' education levels.