Abstract
Teacher quality is widely believed to be important for education, depsite substantial but inconsistent evidence that teachers' credentials matter for student achievement. To accurately measure variation in achievement due to teachers' characteristics—both observable and unobservable—it is essential to identify teacher fixed effects while controlling for fixed student characteristics and classroom specific variables. I find large and statistically siginificant differences among teachers: moving up one standard deviation in the teacher fixed effect distribution raises both reading and math test scores by approximately .1 standard deviations on a nationally standardized scale. In addition, teaching experience has statistically significant positive effects on reading test scores, controlling for fixed teacher quality.