Good teachers form the foundation of good schools, and improving teachers' skills and knowledge is one of the most important investments of time and money that local, state, and national leaders make in education. Yet with the wide variety of professional development options available, which methods have the most impact on student learning? Research on professional development is scattered throughout subject areas, with its focus ranging from classroom processes and structures to teachers' personal traits. "Research Points" has limited this review to learning opportunities for teachers that are explicitly aimed at increasing student achievement. Studies suggest that the more time teachers spend on professional development, the more significantly they change their practices and that participating in professional learning communities optimizes the time spent on professional development. Changing goals for learning, coupled with shifts in curriculum emphasis and a deeper understanding of teacher learning and student thinking, have led to new findings about the impact of teacher professional development and how best to sharpen teachers' skills and knowledge.