This article reports on strategies used by immersion teachers to modify their speech in order to maintain the use of the target language while sustaining interactive communication and the concomitant teaching of the content and the second language. This classroom-based research, undertaken at Methodist Ladies College (MLC) in Melbourne, sources data from selected video transcriptions of three Year 8 French immersion history classes. The selection of samples of teacher talk serves to highlight teachers' discourse modifications designed to facilitate learners' comprehension, negotiation of meaning, and the maintenance of the target language in the classroom. In the examples throughout the text, T is used to indicate the teacher and S the students. This study has allowed identification of some of the main modifications that can be made of teacher talk in a typical immersion class. These modifications were made according to the teacher's judgment of the students' understanding and of their linguistic competence. They served the purpose of linguistic clarification as well as teaching content. These analyses also demonstrate that these strategies are mostly used in combinations to ensure greater success. Using these strategies, the teacher maintained an interactive and communicative classroom despite teaching content that was sometimes daunting in its linguistic and conceptual complexity. In this context, the teacher can be described as the "mediator" as defined variously by Duffy & Roehler, 1986; Newman, Griffin, & Cole,1989; and Tharp & Gallimore, 1988. That is, the teacher has a role to continuously monitor the content and linguistic knowledge of the student. (Contains 2 tables.)