We used a situative perspective to examine teachers' perceptions of a professional development intervention that integrated lesson study, video clubs, and animation discussions. The analysis of interviews with the five geometry teachers who participated in the intervention during two consecutive years showed three characteristics of professional development that were valuable: designated time to collaborate, focus on student mathematical thinking, and use of animations to represent practice. A fourth characteristic, accountability for implementation, is also discussed. The findings have implications for designing professional development, because participants cited links between their experiences and changes in their practice. [For complete proceedings, see ED581294.]