Lesson study is a form of professional development where a group of teachers identifies a problem of practice on which they would like to make progress in their teaching. Over an extended period of time, the teachers study the topic and plan a lesson together. One member then teaches the lesson while the others observe; the group reflects afterwards on student learning. The cycle repeats, building teachers' professional knowledge and their shared views of pedagogy over time. In this article, we argue that lesson study is a collaborative form of practitioner research and we show how this is so by sharing an example of a lesson study cycle conducted in a synagogue school.