Title: Do high-school teachers really matter?
Description: "Unlike in elementary schools, high school teacher effects may be confounded with unobserved track-level treatments (such as the AVID program) that are correlated with individual teachers.  I present a strategy that exploits detailed course-taking information to credibly estimate the effects of 9th grade Algebra and English teachers on test scores.  I document substantial bias due to track-specific treatments and I show that traditional tests for the existence of teacher effects are flawed.  After accounting for bias, I find sizable algebra teacher effects and little evidence of English teacher effects.  I find little evidence of teacher spillovers across subjects"--National Bureau of Economic Research web site.