In this paper, we examine how journal and ethnography field notes in Jugyou Kenkyu (lesson study) help teachers to understand the diverse range of talents and abilities of their students. Especially, we focus on how ethnography field note and reflective papers (karate) help teachers to change their assumptions about student learning. The data presented in this paper come from our research in Ando Elementary School, a typical municipal elementary school in Shizuoka, Japan. We employed a case study method for data collection and a qualitative approach for teaching analysis. We examined the effect of ethnography field notes on the teachers' assumptions about students. Our analysis of the data from various perspective and viewpoints provides insight into the professional development of teachers who participated in Jugyou Kenkyu. [This article appeared in Comparative Education in Teacher Training, v4, p116-125.]