Judging Teachers (Yet Again)

A teacher's "value-added" is defined as the average test-score gain for his or her students, adjusted for differences across classrooms in student characteristics (such as their previous scores). Is teacher value-added a good measure of teacher quality?

That is the question three economists asked in a study, "The Long-term Impact of Teachers: Teacher Valued-Added and Student Outcomes in Adulthood."  A study that got quite a bit of media attention, but made me simply sigh because yet again the f...