Nicholas Kristof thinks the Chicago teachers union is wrong to fight so hard against more stringent teacher evaluations, but he also offers this important observation:
In fairness, it’s true that the main reason inner-city schools do poorly isn’t teachers’ unions, but poverty. Southern states without strong teachers’ unions have schools at least as lousy as those in union states. The single most important step we could take has nothing to do with unions and everything to do with providing early-childhood education to at-risk kids.
Not all school districts are unionized, and the balance of the evidence suggests very little difference in student performance between unionized and nonunionized districts. You're still welcome to approve or disapprove of teachers unions on other grounds, of course, just as you're welcome to think that we should use the results of standardized tests as a basis for evaluating teachers and firing the bad ones. (This is Kristof's view.) It's a fraught subject with evidence that points in both directions, and personally, I'm more skeptical than Kristof. My own read of the evidence is that the value of standardized tests as a way of evaluating teacher performance has enough problems that we should approach it very slowly and methodically. For now, it should probably be no more than a small portion of any evaluation method.
But even if you're more gung-ho on standardized tests than I am, you should know that the evidence doesn't really back up the claim that union-coddled burnout cases are a big contributor to poor student outcomes. They can fire teachers in Georgia a lot more easily than they can in Illinois, but that hasn't improved their schools any. The stubborn fact is that Georgia kids don't score any better on national standardized tests than Illinois kids do.