July 20, 2015 FiveThirtyEight
John Friedman in FiveThirtyEight, "The hard part, as Friedman says, is to “make sure that when you rate a teacher, that you actually rate what the teacher has done, and not whether they had a bunch of very poor or very rich students.”
"The Science Of Grading Teachers Gets High Marks" - FiveThirtyEight