The first time the author was responsible for planning a districtwide professional development day, DuFour secured a funny speaker, provided plenty of doughnuts, and made sure everyone could return to their classrooms in the afternoon. "The day was considered a huge success," he notes. "There was absolutely no evidence that the day had influenced teaching or learning in any way, nor was there any expectation that it should have." But professional development has come a long way since then. Research shows that professional learning communities (PLCs) provide the best environment for powerful professional development and that the best professional development builds staff capacity to function as members of a high-performing PLC. Profiles of several effective PLCs show administrators and teachers working in learning teams within a school, across schools districtwide, and in virtual learning networks.