Good teaching matters. There is persuasive evidence that students benefit from high quality instruction and that these benefits are cumulative for students who have good teachers for several years. Teacher effectiveness matters so much that low-income students lucky enough to have three very good teachers in a row in elementary school earn test scores that, on average, are similar to middle-class children. Conversely, almost all children, regardless of their socio-economic status, will be harmed academically by poor teaching three years running. Nearly 3.8 million teachers work in schools, but there are simply not enough good ones to go around, especially in the schools and districts serving high-poverty, large-minority student populations. And although one focal point of the No Child Left Behind (NCLB) Act of 2002 was to address this problem, the policies states developed in response to NCLB's call have not achieved this goal. The quality of teaching is not simply determined by an individual's knowledge or ability, but also by the contexts in which teachers work. Improving teacher quality thus entails policies concerning recruitment, early preparation, retention (including attention to working conditions), as well as professional development. This paper provides recommendations that address each of these domains. (Contains 32 notes.)