This paper addresses potentially problematic classroom episodes in which someone foregrounds a social division that is normally taken for granted. It illustrates the way in which linguistic ethnography can unpack the layered processes that collide in the breaking of silence, showing how linguistic form and practice, individual positioning, local institutional history and national education policy development all count, and it discusses the value of situated interactional data for teacher development. It presents two case studies, involving a Turkish language class in a Greek-Cypriot secondary school, and a discussion of Standard English in an inner London comprehensive.