Test scores, the argument:
News media says American education compares poorly to other countries on standardized tests. People want someone held responsible. Standardized tests measure students’ learning. Teachers are the ones who are responsible for that lack of learning. Let’s use standardized tests to fire teachers whose students get bad tests scores, and then hire better teachers to replace them.
American education aims to work with the whole child, and to educate every child, offering frequent opportunities for moving between educational tracks. Americans value freedom and choices over stability and standardization. Other countries value stability and standardization, tracking students irreversibly, usually early in their academic careers. If you are a poor test taker, and you decide in 10th grade you want to be a doctor, it may be way too late. Finally, almost every American student takes these standardized tests. In other countries, special ed or vocationally tracked students can be left out of testing (or school) completely.
Standardized tests don’t just measure teacher performance. They also measure student interest, mental and physical health, parental support, and neighborhood safety. How can you control for those factors, which are completely out of the teacher’s control, from the data? What if kids change schools? The poorest kids change schools the most, so they’re really screwed. (For statistics folks, sample sizes are too small, and too variable.) It’s already damn difficult to staff the toughest schools. Turnover is near constant. Those teachers often get paid less, and their jobs are harder. You can fire all the teachers whose students get bad test scores, but who is going to replace them? What makes you think those new people will do a better job, or that a better job is even possible?