We argue that 'academic language' should not be understood as technical components associated with a 'register', and that instead we must attend to its enregisterment. Enregisterment relies upon language ideologies and models of personhood, requiring attention to social components of 'academic language' beyond lexico-grammar. We draw on ethnographic data from Latina girls in a US middle school to show how adolescence presents a unique ontogenetic stage that influences how language use becomes enregistered. We show how language is enregistered in middle school differently than in elementary and high schools. Focusing on how language use becomes recognizable and indexically linked to social types, we show how 'academic language' is one way through which race, gender, and other socially identifiable positionalities are achieved. Adolescence may present a unique opportunity for intervention as students' experiences with language and racialization become increasingly generalized.