The mission of the National Board for Professional Teaching Standards (NBPTS) is to establish "high and rigorous standards for what teachers should know and be able to do, to certify teachers who meet those standards, and to advance other education reforms for the purpose of improving student learning in American schools." In response to a request from the U.S. Congress, the National Research Council developed a framework for evaluating programs that award advanced-level teacher certification and applied that framework in an evaluation of the impacts of the NBPTS. Specifically, this book addresses the impacts on students, teachers, and the educational system in this country. Assessing Accomplished Teaching finds that teachers who earn board certification are more effective at improving their students' achievement than other teachers, but school systems vary greatly in the extent to which they recognize and make use of board-certified teachers. Many of the questions on the evaluation framework could not be answered because the data have not been collected, and the report makes recommendations for the kinds of research that are needed to fully evaluate the impacts of board certification by the NBPTS.