Lesson study, a form of school-based professional development widely practiced in Japan, has gained popularity in the United States over the last two decades. However, research on its effectiveness has been limited in scope, typically conducted shortly after the conclusion of the professional learning and focused primarily on the practices of individual teachers.

This study explores and analyzes the lingering effects of a form of lesson study, the Studio Classroom Project, on both the individual teaching practices and collaborative work of two middle school mathematics departments. I conducted this descriptive case study over a year after teachers participated in the original project. I collected data using the following methods: individual interviews with participating teachers and principals, as well as with consultants who facilitated the projects at the sites; and a series of classroom observations of selected teachers at each site, using structured instruments to collect data on student discourse and classroom context, structure, and activities.

The findings suggest positive effects on teachers’ practices, including the use of inquiry-based classroom structures and activities. However, while the amount of student discourse proved high, discourse at lower cognitive levels predominated. Additionally, data from the schools’ summative assessments did not indicate increased success in student learning. Findings related to the effectiveness of teachers’ work in Professional Learning Communities were more uniformly positive. Teachers in both departments expressed strong commitments to student learning, and data from both interviews and observations reflected high levels of collaboration and professionalism.