This article explores the ways in which what counts as "legitimate" knowledge is produced and negotiated in two multilingual classrooms of two different programmes designed to "attend to diversity" at secondary schools in the Madrid region. Following a sociolinguistic approach, the article focuses on the ways in which local identities, beliefs and social relations emerging from situated practice become a window through which to understand how different social experiences and academic trajectories are institutionally constructed in connection with broader social processes. For this reason, the article seeks to connect recorded and observed classroom interactional patterns, through which "legitimate" knowledge is produced, with social actors' (teachers and students) positioning(s), and the academic trajectories of students enrolled in such programmes. We end with a discussion about the possible consequences of such practices for migrant students, recently arrived in the Madrid classrooms, in terms of academic success and school participation.