Since 2007, Center for Research in Mathematics Education had started implementing the lesson study and open approach in Nongtoom-nong-ngu-lerm School, and Ban-Beung-neum-be- ung-krai-noon School were funded by the Office of The Basic Education Commission in Research Program on “Model for Fostering Students’ Mathematical Thinking by Implementing Lesson Study and Open Approach”. I and team introduced our information to teachers and teacher introduced team to students in the classroom. The team could implement following processes of lesson study and open approach, observe behavior of students both inside and outside classroom as participation observation, record video and audio tap in the classroom and reflect students’ thinking in school meeting every week. In 2009, these schools were funded by the Office of The Basic Education Commission in Project for Professional development of Mathematics teachers through Lesson Study and Open Approach. I used participation observation and informal interview to find target group in this research. I record my data following my framework at Nongtoom-nong-ngu-lerm School in 2009 and at Ban-Beung-neum-beung-krai-noon School in 2010 by recording video and audio taps. Video provided a more comprehensive understanding of the students’ learning. I reviewed the video and audio taps to select data and posing problem which brought opening them and asked students in interviewing students. Data analysis used video analysis supported by protocol analysis, and used analytical description for students’ behavior in mathematical communication by gesture to analysis data.