Video is currently a key element of numerous professional development programs, yet relatively little is known about how video fosters changes in teachers' thinking. This study examines how a particular type of video-based professional development, namely video clubs, supports teacher development. Video clubs are professional development environments in which groups of teachers come together to view and discuss videos of one another's teaching. In this paper, we study how two different video club designs support teachers in "learning to notice" classroom interactions in new ways. Data for this study include a pre- and post-interview conducted with each participating teacher from the two video clubs. Analysis reveals that, for one group, the scope of their comments became focused on a particular issue, interpreting the mathematical ideas expressed by students in the video excerpts. In contrast, the second group developed a range of perspectives for discussing the video segments. We argue that the different designs of the video clubs influenced the ways in which the two groups of teachers "learned to notice." (Contains 6 tables and 8 footnotes.)