This study aimed to investigate the effectiveness of Pedagogical Content Knowledge-Guided Lesson Study (PCKLS) as an intervention to develop PCK competencies among teachers and consequently enhance student achievement in terms of conceptual understanding and problem-solving skills. Using quasi-experimental design, teacher competencies and student achievement in the PCKLS group and the conventional group were compared. In the PCKLS group, the intervention involved planning the lesson by the research team, teaching the planned lesson while PCK observations were made by the researcher and another teacher from the group, including a feedback meeting, implementing the improvements in the reteach stage of the lesson study cycle by another teacher...