Teachers are paid to teach. We measure worker productivity of teachers by measuring the retained info, improved attitudes, and developed skills in the students that got the teaching. We use standardized tests. If too many students flunk we need to find more productive teachers. The crappy teachers will always find jobs being hired by idiots who say "wow! what a great school, everyone flunked!!".
IMHO Princeton's problem is that it's caring more and more about community politics and less and less about getting back to the hard work of teaching.