Professional community among teachers, the subject of a number of recent major studies, is regarded as an ingredient that may contribute to the improvement of schools. The research reported in this article is grounded in the assumption that how teachers interact with each other outside of their classrooms may be critical to the effects of restructuring on students. The analysis focuses on the type of professional community that occurs within a school and investigates both the organizational factors that facilitate its development and its consequences for teachers' sense of responsibility for student learning. The findings suggest that wide variation in professional community exists between schools, much of which is attributable to both structural features and human resources characteristics, as well as school level. Implications for current school reform efforts are discussed.