Recent research on teacher education has highlighted the importance of teachers' noticing of students' mathematical thinking. Much remains unknown about the ways in which teachers develop noticing abilities in professional development settings. This study examines changes in teachers' noticing in the context of peer discussions in a video club. The study identified "critical incidents" of noticing, ranging from attending and interpreting to deciding on pedagogical responses. Furthermore, the study divided "attending" in the noticing framework into "selecting" and "recognizing." Findings indicate that peer discussions about a video showing students' statistical variability reasoning catalyzed change in teachers' attending. Other catalysts include (1) participants' assumption of the proposer role in the video club, (2) participants' peers as the coadjacent speakers, and (3) participants' use of an analytical framework as professional knowledge. The study discusses the ways in which participants' individual focal components of noticing emerge and develop through a video club as professional development.