Ranking Teachers when Teacher Value-Added is Heterogeneous Across Students

The typical measure used by researchers and school administrators to evaluate teachers is based on how the students' achievement increases after being exposed to the teacher, or based on the teacher's "value-added''. When teacher value-added is heterogeneous across her students, the typically used measure reflects differences in the average value-added the teacher provides. However, researchers, administrators, and parents may care not just about the average value-added, but also its dispersion. In this paper, I examine the robustness of typical teacher quality measures to alternate ranking systems factoring in the variance of value-added. Encouragingly, ranking systems factoring in the variance produce similar rankings as the ranking system based only on the mean. I also examine whether classroom characteristics and teacher experience affect a teacher's value-added variance and find that they explain little of the variation in value-added variances.