In a professional learning community (PLC), teachers are organized into teams, committed to meeting on a regular basis to study their teaching strategies and the effects of those strategies on the students in their classrooms. The teacher teams can be of varied form and composition. Whatever the organizational structure, the teams have one goal - that is to improve teaching so that student learning is improved. Policy developers, legislators, and educational leaders have encouraged the adoption of collaborative professional learning teams as a school reform model for improving schools. In this book we describe the results of studies of professional learning communities in real schools and the effects of the teams on student learning. Much of the time school innovations are not examined in depth. Instead authors and developers simply advocate that they be used. In this book, school principals and administrators describe how their teachers used the PLC teams to improve student learning in their schools. In other words, this book presents actual research on the effects of the use of PLCs rather than testimonials.