Mathematical prescriptivism is a language ideology found in school mathematics that uses a discourse of rationality to proscribe language forms perceived as illogical or inefficient. The present study is based on a three-year ethnographic investigation of Math Corps, a community of practice in Detroit, Michigan, in which prescriptive language in the classroom is used both to highlight beneficial algorithms and to build social solidarity. Although motivated by the analogy with English orthographic reform, prescriptivism at Math Corps avoids potentially harmful criticism of community members of the sort often experienced by African American students. A playful linguistic frame, the prescriptive melodrama, highlights valued prescriptions, thereby enculturating students into the locally preferred register, the ‘Math Corps way’, which encompasses social, moral, linguistic, and mathematical practices and norms. A sociolinguistic and anthropological perspective on prescriptivism within communities of practice highlights positive alternatives to the universalizing prescriptions found in other English contexts. (Prescriptivism, language ideology, mathematics education, community of practice, Math Corps, linguistic anthropology, language socialization)*