This article examines the underprobed co-teaching classroom setting. It examines classroom interactions wherein one American and one Korean teacher at te same time employ English and Korean to perform content-based lessons. The analytic emphasis is on the co-teacher's entry into the second turn position of initiation-response-feedback (IRF) sequences and the actions which the teacher uses in these turns. The sequences display a separate interactional structure that diverges from archetypal IRF sequences, unveiling the participants’ collaborative methods of directing classroom incidents, settling student participation, and achieving the curricular lesson focus.