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The study aims to analyze a lesson study as a model of effective teacher training for improving the quality social sciences teachers in primary school. This research used an approach of descriptive-qualitative phenomenology and the research design used a modified class action-based lesson study. The place of research in Surakarta. The subject of study included the Primary School teachers and the informants were the teachers, principals, supervisors. The data gathering employed questionnaires, interview, and observation. The data analysis used the first order understanding and second order understanding with an interactive model, including data reduction, data display, and conclusion/verification. The results of the research show that; the a lesson study as a model of effective teacher training for improving the quality social sciences teachers in primary school, use ; "a modified lesson study" with three strategy, yaitu; Strategy-based improving the quality of collaborative, Strategy-based improving the quality of issues, and Strategy-based improving the quality of directly. Whereas the effectiveness of the lesson study as model for developing the professional primary school teachers is conducted through the K3S (the Principal’s Working Group) and implemented through the KKG (the Teachers’ Working Group),