Just because it's difficult to find out doesn't mean we shouldn't try. No performance system is perfect but by at least trying to figure it out we'll have a bet

Just because it's difficult to find out doesn't mean we shouldn't try. No performance system is perfect but by at least trying to figure it out we'll have a better system than we have now. I, for one, know which of my prior teachers have been good and which haven't and most of my classmates would agree. Asking former students may be one idea although it's a pretty slow feedback cycle. You wouldn't be able to ask students immediately after the year is over since it would probably be correlated to the grade they received but years down the line people would have a pretty good sense of who the good teachers they had were. One can also have former teachers monitor more as well as have more frequent observation sessions. I'm sure there are tons of ideas people have and it's important to choose the best ones but none of this is going to happen until we make it a point to pay for performance. In a way, it's similar to startups - you don't know what the final product is and you can always improve but it's important to start in order to get the feedback, learn from it, and iterate on the product.