Leading whole-class discussion requires teachers to balance careful preparation with improvisation based on students' contributions. How do teachers learn to engage in the difficult work of orchestrating a rich and, by nature, improvised classroom discussion? How might training in improvisational theatre affect teachers' facilitation of discussion? This paper addresses these questions by examining a series of discussions led by a high-school history teacher before and after his participation in an improv course. Data sources included videotaped observations of classroom discussion, audiotaped interviews, and field notes and recordings of selected activities from the improv course. Results suggest that the improv course supported the teacher's development of new approaches to discussion.