<p>Vygotsky proposed that pretend play in early childhood contributes to growth in self-regulation in two ways. First, in such play, children must adhere to the rules of make believe situations, especially when they take on mature pretend roles. Second, they must conform to rules agreed upon by all players when interacting with peers. In the present investigation, these two theories are tested by examining the independent associations of 33 preschool children’s solitary pretend play and social pretend play with inhibitory control (IC), as measured by the Day/Night Stroop Test (MacLeod, 1991). This IC measure was administered individually to participants at the beginning and end of the study. Their naturalistic play in their classroom’s dramatic play and block centers was then observed and coded over six months to determine frequencies of solitary and social pretend play. In a regression analysis, we first fitted a model with pre-study IC measures, age, SES, and gender as independent variables and IC post-study scores as the dependent variable. All of these independent variables were found to be significantly related to IC. We then fitted a second model in which we added pretend play frequencies along with these other variables. Frequency of overall pretend play was found to explain 3% of growth in IC. However, only social pretend play was found to significantly contribute to IC growth. Implications for preschool classroom practice, including the importance of fostering pretend play with peers, are considered.</p>