The central focus of the research reported here was to investigate the usefulness of peer interaction on the development of reflective ability and teaching knowledge of two secondary mathematics teachers. Tracing the fate of two secondary mathematics teachers in a teamed field-based discussion experience over the course of 12 weeks, the findings of the research indicate that the use of peer discussion has the potential to facilitate reflective ability development and teaching knowledge development. Peers helped each other to identify teaching issues, teaching actions, and mathematics understanding of students. Their level of reflection increased in the process of peer discussion. Using a tool for evaluation of teaching guided the direction of reflection but limited the scope of discussion.