Teacher quality might matter

Ed Sector has put out a new report, purporting to show that in Illinois, students do worse if they have lower-quality teachers (as measured by the teachers’ average test scores, qualifications, etc). Unfortunately, while the conclusion seems sensible, I don’t trust the analysis. The measure of teacher quality is the average teacher quality at a school. And schools where teachers have lower qualifications are probably also places where students are poorer, have more problems at home, and so on. The right way to do this would be to look within a school, but the researchers clearly don’t have that data. This is one of those instances that illustrates how important teacher quality might be, and how hard it is to look at it properly.