Teacher evaluation systems are being overhauled by states and districts across the U.S. And, while intentions are admirable, the result for many new systems is that good, often excellent, teachers are lost in the process. In the end, students are the losers. In her new book Linda Darling-Hammond makes a compelling case for a research-based approach to teacher evaluation that supports collaborative models of teacher planning and learning. She outlines the most current research informing evaluation of teaching practice that incorporates evidence of what teachers do and what their students learn. In addition, she examines the harmful consequences of using any single student test as a basis for evaluating teachers. Finally, Darling-Hammond offers a vision of teacher evaluation as part of a teaching and learning system that supports continuous improvement, both for individual teachers and for the profession as a whole.