The following information is from the Research for Better Schools website
          http://www.rbs.org/lesson_study/
        
        Many professional organizations promote teacher collaboration, but lesson   study goes beyond collaboration to co-planning and observing actual lessons with   a focus on student thinking. In the lesson study model of ongoing professional   learning, teachers learn together, with administrators and specialists, and even   with other schools. Participants plan, observe, and refine "research lessons"   designed to make real their long-term goals for student learning and   development.
        A key, concrete component of lesson study is the observing and teaching of   lessons, which then are improved collaboratively. The real "lesson" of lesson   study is not product, but process. It compels teachers to examine their own   practice in depth in the context of student learning, connects them with their   students and their professional community, and inspires them to improve   continually. This model of ongoing, teacher-led professional development has   been applied most successfully and widely in Japan. It has recently been adapted   and initiated by teachers at many sites across the U.S.