This paper describes strategies used by novice biology teachers to exert sociolinguistic control over conversations when teaching unfamiliar subject-matter content. These discourse control strategies were identified in a year-long study of teacher subject-matter knowledge and its effects on teaching, and are illustrated in three lessons taught by one of the teachers in the study, two on unfamiliar content and one on familiar content. The findings corroborate two parallel analyses of teaching that focused on curricular planning and statistical study of teachers' utterance-by- utterance speech.