The purpose of this study was to explore the role of social preference and perceived acceptance as moderators of the relation between child temperament and externalizing behavior. Participants included 399 children evaluated at pre-kindergarten and kindergarten assessments. Pre-kindergarten children characterized by high temperamental Surgency/Extraversion were more likely to exhibit hyperactivity and aggression in the kindergarten classroom. In addition, kindergarten perceived acceptance and social preference moderated the relation between pre-kindergarten Surgency/Extraversion and kindergarten hyperactivity for girls only. Girls who were characterized by high temperamental Surgency/Extraversion, high perceived acceptance, and low social preference were at risk for higher levels of teacher-reported and peer-nominated hyperactivity. In contrast, accurately high perceived acceptance was a protective factor for high temperamental Surgency/Extraversion. Findings are discussed in terms of risk and protective factors for externalizing behavior. (Contains 3 tables and 3 figures.)