In this paper, the authors use a ten-year span of longitudinal data from North Carolina to explore a range of questions related to the relationship between teacher characteristics and credentials, on the one hand, and student achievement on the other. They conclude that a teacher's experience, test scores and regular licensure all have positive effects on student achievement, with larger effects for math than for reading. Taken together, the various teacher credentials exhibit quite large effects on math achievement, whether compared to the effects of changes in class size or to the socioeconomic characteristics of students.