Research on teacher quality is not definitive. But, we know that developing high-quality teachers requires a multipronged approach: We need to recruit promising teachers. We need to retain and reward effective early career teachers. We need mechanisms to dismiss those who don't improve. We need to focus teacher preparation on the foundations of skilled beginning practice, and we need to invest in systems of professional development that effectively improve the practice of experienced teachers. We also need to invest in working conditions, which are fundamentally tied to school climate and resources.