One of the key provisions of the No Child Left Behind Act requires states to ensure that every teacher be “highly qualified.” Though the meaning of “highly qualified” remains hotly contested, the legislation's emphasis on teachers is well founded. Nearly all modern research on the subject finds teacher effectiveness to be among the most important school inputs into student achievement. Yet recent literature, including my own work (Corcoran, Evans, and Schwab 2004), finds evidence that the quality of teachers has steadily eroded over time. In particular, the likelihood that a high-aptitude female pursued a career in teaching dropped precipitously between 1960 and 2000. In this article, I summarize these and related findings, review some of the most common explanations for the trend in teacher quality, and discuss policies that have been advanced to attract talented graduates to the teaching profession.