This paper examines a group of secondary mathematics teachers who met 16 times to discuss video excerpts of their teaching. The explicit purpose of the meetings was to assist the teachers in preparing video for submission to the National Board for Professional Teaching Standards. Analysis of meeting transcripts reveals that teachers engaged in intensive discussions about mathematical discourse. Specifically, the teachers investigated three discourse-related themes: techniques for facilitating discourse, contextual factors affecting discourse, and criteria for evaluating discourse. The meetings also supported the development of a professional community among participants as they collaboratively and substantively examined each other's practices. This research adds to our understanding of teacher professional development and provides particular insights about how preparing for National Board Certification can facilitate teacher learning and the development of professional teacher communities. (Contains 3 notes and 3 tables.)