Children's achievement-related theories have a profound impact on their academic success. Children who adopt entity theories believe that their ability to perform a task is dictated by the amount of natural talent they possess for that task--a belief that has well-documented adverse consequences for their achievement (e.g., lowered persistence, impaired performance). It is thus important to understand what leads children to adopt entity theories. In the experiments reported here, we hypothesized that the mere act of linking success at an unfamiliar, challenging activity to a social group gives rise to entity beliefs that are so powerful as to interfere with children's ability to perform the activity. Two experiments showed that, as predicted, the performance of 4- to 7-year-olds (N = 192) was impaired by exposure to information that associated success in the task at hand with membership in a certain social group (e.g., "boys are good at this game"), regardless of whether the children themselves belonged to that group.