Private Islamic schools in Southern Thailand face significant challenges, particularly in adhering to national educational standards, which impacts students’ academic outcomes. Most Islamic Studies teachers lack formal pedagogical training, resulting in a teaching approach that often fails to engage students effectively. This study employed participatory action research (PAR) involving 32 Islamic Studies teachers across 10 schools. The research was structured around the four phases of PAR: establishing relationships, collaborative design, implementation through LS and Open Approach, and reflective assessment. The implementation of Lesson Study and Open Approach led to significant improvements in teaching practices, shifting from traditional teacher-centered methods to learner-centered approaches that emphasized critical thinking, self-directed learning, and the integration of ICT. This study demonstrates that adapting LS to the context of Islamic education can enhance professional development for teachers and improve educational outcomes. This approach could serve as a model for broader educational reforms in the region.