The objective of this research was to explore the Mathematical Communication by 5th grade students’ gestures in Lesson Study and Open Approach context. This study was conducted at Nongtoom-nong- ngu-lerm School, and Ban-Beung-neum-beung-krai-noon School, Muang District, Khon Kaen Province in Project for Professional development of Mathematics teachers through Lesson Study and Open Approach, using qualitative research: Ethnographic Study, in-depth interview, Video Analysis supported by protocol analysis, and Descriptive Analysis. The research findings found that there were 7 kinds of students’ Mathematical Communication by students’ Gestures including 1) rigorousness by students’ beat gesture; 2) rigorousness by students’ metaphoric gesture; 3) economy by students’ deictic gesture; 4) economy by students’ iconic gestures; 5) freedom by students’ deictic gesture; 6) freedom by students’ iconic gesture; and 7) freedom by students’ deictic and iconic gestures in explaining students’ Mathematical Ideas, and the most commonly used economically by deictic gestures, and students’ self learning in Open Approach. Furthermore, the schools in Lesson Study and Open Approach context, the students had opportunity in learning based on their potentiality, being able to think, perform, and express. They preferred to express divergent think.
Keywords: Mathematical Communication; Gesture; Lesson Study; Open Approach