This paper examines one model of professional development, the use of video clubs in which groups of teachers watch and discuss videotapes of their classrooms. Specifically, the paper investigates the learning that occurred as four middle-school mathematics teachers participated in a year-long series of video club meetings. Over time, discourse in the video clubs shifted from a primary focus on the teacher to increased attention to students' actions and ideas. In addition, discussions of student thinking moved from simple restatements of students' ideas to detailed analyses of student thinking. Furthermore, teachers began to reframe their discussions of pedagogical issues in terms of student thinking.