ABSTRACT
This research was under context of professional development for mathematics teacher by using the innovation of lesson study and open approach project implemented by the Center for Research in Mathematics Education, Faculty of Education, Khon Kaen University, during 2009-2011 academic years. The objective of this research was to study the development of mathematical knowledge for teaching of teacher from working based on 3 steps of the lesson study cycle that incorporated 4 phases of open approach. The target groups were a lesson study team in a project school. Data were collected from 3 steps of lesson study and analysis procedures were based on analyzing videos, protocols, and descriptive analysis. The research found that the teachers obtained development as follows: 1) during the step of collaboratively design research lesson, they discussed and shared knowledge in the mathematical textbooks of project, discussion in objective of the lesson and construction of open-ended problem situation, anticipation for students’ thinking, and specification of issues for discussion in classroom; 2) in the step of teaching and collaboratively observing the research lesson, they obtained knowledge for teaching by presenting the open-ended problem situation, the occurred difficulty of students’ problem solving, the students’ thinking approach in problem solving, the association of approach in each learning unit, the sequencing of thinking, and the extension of students’ incomplete thinking approach; and 3) during the step of collaboratively reflection on teaching practice, teachers obtained knowledge by reflecting the students’ goal accomplishment, the students’ learning process, the students’ thinking approach, the efficiency of media, and the experts’ recommendations.