Research suggests effective professional learning communities (PLCs) enhance teacher collaboration and student achievement. Within-school variation in PLC processes, however, is underexplored. This study highlights differences in teacher behavior and teams' perceptions of principal leadership in well-functioning teams versus less well-functioning ones. Analysis of interviews of principals and team members showed teams differed in intensity of analysis of student work and the level of changes in instructional practices. High-functioning teams felt supported by the principal while the less well-functioning teams did not. These findings suggest the need for more active principal facilitation of PLCs to achieve full benefits.