Lesson study has been a central organizing framework for the year-long MCMS [Mid-Career Math and Science Program at Mills College] Curriculum and Instruction (C & I) class for three consecutive spring semesters. Lesson study was adopted to facilitate student development in four primary ways. First, lesson study is intended to showcase and provide hands-on experiences with thorough lesson planning and revising at a level student-teachers would otherwise not experience. Second, through the lesson study inquiry cycle, student-teachers clarify and define their 2 own vision, goals, and objectives for students. Third, by building on shared experiences and diverse interpretations of classroom events, lesson study provides rich opportunities for understanding and talking about students and learning. Fourth, lesson study was adopted to provide a structure for and robust definition of collegiality, based on formal protocols and teachers’ diverse and interdependent expertise.