Despite Australia's strong tradition of research on language maintenance and shift, little is known about the ways in which migrant background students continue to use their heritage languages in Australian schools. This paper presents an in-depth case study of students' linguistic practices at a multiethnic Melbourne high school, where over 95% of students speak a language other than English (LOTE) at home. Although virtually all students are bilingual, it shows that peer group divide sharply on linguistic lines, with recent arrivals from China and Sudan the only students to consistently speak their first languages with friends at school. More established students use English as their lingua franca with friends, but continue to deploy their LOTEs for a variety of purposes, including gossiping, crossing and communicating with recent migrants. The paper argues that while established students make only incidental use of their LOTEs at school, LOTE use performs important social functions for these students that could not be substituted by using English alone. Local conditions at the school clearly shape the meanings ascribed to LOTE use; and the paper thus argues that detailed analysis of students' linguistic practices can be a valuable tool for examining interethnic relations in multiethnic schools. (Contains 1 table and 4 notes.)