Teacher Performance, can it really be "measured"?

The Duluth News Tribune published my "Local View" with the title "Teacher Performance has always been variable". You can find it at http://www.duluthnewstribune.com/event/article/id/221673/

I wrote it in light of all the bashing of teachers that has been going on and of the notion that you can judge performance at the end of a school year. I really think teachers should be paid like insurance agents - instead of a cut of the ongoing premiums they get a cut of the income taxes their former students pay.