This qualitative study, which includes interviews with principals and teachers and observations of professional development activities, teacher team meetings, and technical support consultations, concludes that the work of teacher professional communities can be divided into two categories. The supportive practices of teacher teams are related to achieving the daily tasks required of individual teachers, such as addressing students' behavioral and learning problems. Developmental practices are related to improving instruction and curriculum schoolwide, and include planning, implementing, and monitoring interventions geared toward improving student performance.