This article presents a professional development initiative developed by a university-school partnership based on the Japanese lesson-study model described by Stigler and Hiebert (1999) in "The Teaching Gap." Lesson study ("jugyoukenkyu"), an inquiry model of teacher professional development, is used extensively throughout Japan and has begun to capture the attention of the American educational community as a potential strategy for enhancing teacher professional development in America. The study presented in this article aims to describe the effects of the lesson study process on six upper-elementary teachers from a city school system in the southeastern United States. The study specifically addresses the following research questions: (1) How do these teachers perceive lesson study as a professional development process?; and (2) How will engaging in lesson study affect these teachers' instruction? The findings of this study suggest that the lesson study process embodies the core features of professional development experiences identified by Garet, et al. (2001) that have significant positive effects on increased teacher knowledge and skills and changes to instructional practice. The sustained, on-going nature of the lesson study experience, involving the processes of researching, collaborating, active learning, observation, and focused reflection and discussion, led to professional growth that these participants believe will have lasting impact on their instructional practices. This study also suggests the importance of having someone serve as lesson study facilitator to guide the process, organize resources, and assist in finding coverage for classrooms to allow for teacher planning, observations, and reflection/critiquing sessions.