The effectiveness of the "Tools of the Mind (Tools)" curriculum in improving the education of 3- and 4-year-old children was evaluated by means of a randomized trial. The "Tools" curriculum, based on the work of Vygotsky, focuses on the development of self-regulation at the same time as teaching literacy and mathematics skills in a way that is socially mediated by peers and teachers and with a focus on play. The control group experienced an established district-created model described as a "balanced literacy curriculum with themes." Teachers and students were randomly assigned to either treatment or control classrooms. Children (88 "Tools" and 122 control) were compared on social behavior, language, and literacy growth. The "Tools" curriculum was found to improve classroom quality and children's executive function as indicated by lower scores on a problem behavior scale. There were indications that Tools also improved children's language development, but these effects were smaller and did not reach conventional levels of statistical significance in multi-level models or after adjustments for multiple comparisons. Our findings indicate that a developmentally appropriate curriculum with a strong emphasis on play can enhance learning and development so as to improve both the social and academic success of young children. Moreover, it is suggested that to the extent child care commonly increases behavior problems this outcome may be reversed through the use of more appropriate curricula that actually enhance self-regulation. (Contains 8 tables.)