Purpose: This research explores the "transformation" ideas of Japanese Lesson Study (LS) and Open Approach (OA) to create and sustain a Thailand LS incorporated OA (TLSOA) model to successfully adapt to the local contexts. Although LS is spreading globally, previous studies have identified several challenges to its implementation. Design/methodology/approach: The researcher employed a longitudinal research design that involved repeated investigations of a group of participants: from their fourth year as bachelor's degree students until they became eligible coordinators to practice the TLSOA model for teachers' professional development (PD). Data were collected using reflective journals, two types of survey questionnaires, and records of periodical reflective meetings over three cohorts. Findings: As results reveal, the participating teachers' active engagement in the TLSOA model has made a positive impact on their teaching practices, collegiality, and professional self-identification. Students perceived themselves as having enormous changes in their learning behaviors. Those changes are linked to establishing a positive, student-centered, and active learning-based school culture with teachers' beliefs for innovations. Research limitations/implications: Further studies should focus on the possible conflicts emerging between the different cultures of teaching. Practical implications: The idea of the TLSOA model is to ensure teachers are well trained to possess sufficient skills. Originality/value: The findings could be of value for the leaders, educators, policymakers to advocate the TLSOA model as a systematic approach to whole-school improvement and as a channel for spreading effects at the national, the APEC, and the CLMV regional levels.