One of the obstacles to states putting in new evaluation systems which use any test score data is the pushback from teachers. Teachers worry a lot that their rating will depend more on who they teach, than how well they teach.
We can put that argument aside--if we're all willing to acknowledge the results in Florida, where test scores now comprise 50% of a teacher's rating.
Florida has found near-zero correlation between teachers' evaluation scores and the percentages of their students who are poor, nonwhite, gifted, disabled or English language learners. None. The fact that a teacher only is responsible for growing student learning from the baseline scores she inherits from the previous year mitigates any need to make accommodations for students' background.
"Those things didn't seem to factor in," said Kathy Hebda, a deputy chancellor, in testimony to the legislature. "You can't tell for a teacher's classroom, by the way the value-added scores turned out, whether she had zero percent students on free and reduced price lunch or 100 percent."