Student teachers often struggle with handling events in the complex environment that is a classroom. This article reports on a study that investigates the potential of using video-based materials to support mathematics student teachers in developing and applying professional knowledge. Student teachers viewed videos of classroom events with possible teacher reactions to each event. This article reports on the discourse that occurred before and after the viewing of the four possible responses in terms of the content and the nature of the discussions. Results show that when the event focused on mathematics, the focus of the responses shifted from themselves as teachers to the learners. However, the converse was true when the event focused on generic classroom management issues. Additionally, the nature of both sets of responses became more evaluative and interpretive following the video clips of possible responses.