This book elucidates the formation and development of theories of action in school reforms for Schools as Learning Communities (SLC) during ten years from its inception in 1998 in select Japanese elementary schools, junior high schools, and one secondary school. While growing international interest in Japanese lesson study is in pursuit of a standard lesson study, Suzuki offers a unique perspective into school reforms for SLC and how they resisted the standardization of lesson study out of concerns that it would limit a teacher's autonomous judgment and choice. Through a theory-of-action approach in its examination of the pilot schools for SLC, this book clarifies: • Why did teachers reform lesson study? • What were the difficulties in reforming lesson study? • Why were teachers working on school reform for SLC? • Why did the school reform for SLC evolve from an elementary school to the junior high schools and high schools? This book provides a theoretical foundation for reviewing the past efforts and histories of Japanese lesson study reforms, and will interest academics and practitioners looking for insights into the future of lesson study. Winner of the Seiichi Tejima Research Award (2023 Book Award) and the Academic Research Award by the Japan School Improvement Rescarch Association (2022).