We use data on statewide end-of-course tests in North Carolina to examine the relationship between teacher credentials and student achievement at the high school level. We find compelling evidence that teacher credentials, particularly licensure and certification, affects student achievement in systematic ways and that the magnitudes are large enough to be policy relevant. Our findings imply that the uneven distribution of teacher credentials by race and socioeconomic status of high school students--a pattern we also document--contributes to achievement gaps in high school. In addition, some troubling findings emerge related to the gender and race of the teachers. (Contains 9 tables and 32 footnotes.)