it again). 3 At the heart of lesson study is the research lesson, an actual classroom lesson that is designed to teach a particular topic and at the same time bring to life a larger goal or vision of education. The research lesson is observed live by collaborating teachers and carefully documented, usually using multiple methods including videotape, audiotape, observation notes of students, and collection of student work. This collection of data is the pivotal feature of lesson study. Ideally, the data collected during the research lesson reveal what students learned (or didn’t) and what features of instruction led (or failed to lead) to learning. The data provide grist for a lively post-lesson colloquium on how students learn this subject matter, and how the particular lesson and the larger instructional approach need to be revised. Hence, the data collection provides a vital link from one phase of lesson study to the next, as teachers plan, teach, observe, and revise the lesson and the larger approach to instruction. It is the collection and analysis of data that puts the “research” in research lesson. (See Appendix A for a description of the types of research lessons in Japan.)