This post by Andrew Gelman:
From the work of Jonah Rockoff and others, I am convinced that teacher effects are real and they are large. And school effects are mostly the composition of teacher effects. I'm not sure about how large the interactions are (i.e., if some teachers do better with good students and others do better with poor students).
reminded me of something I had previously read from Education Trust that shows that "effective" teachers are very effective. Particularly impressive were some of the charts that show the differences in gain scores for children with "effective" versus "ineffective" teachers. Another presentation also shows the same although the studies they cite are hard to find on the web:
1. Heather Jordan, Robert Mendro, and Dash Weerasinghe, The Effects of Teachers on Longitudinal Student Achievement, 1997
2. Sitha Babu and Robert Mendro, Teacher Accountability: HLM‐Based Teacher Effectiveness Indices in the Investigation of Teacher Effects on Student Achievement in a State Assessment Program, 2003
As such, it was hard to figure out how "effective" was defined. The more traditional definitions using years of experience, certification and degrees was done by Gordon, Kane and Staiger which shows that teachers are important as well.