Charles, this is an issue that we struggle with in medicine too. There is a strong push to rate doctors, but there is huge disagreement as to how to do it fairly. Every doctor, when faced with being ranked on their outcomes, claims that their patients are sicker than their colleagues', and so any comparison would be apples to oranges. This is of course true of some of them, but can't be true of all of them, logically. So we need a way of ranking just how sick the patients are to begin with (or, for teachers, just how much "potential" each student might have?). Another thorny problem is the fact that teachers and doctors and other professionals deal with human beings (as opposed to, say, widgets), and that humans have a way of doing what they want to do regardless of what their teachers or doctors try to persuade or "make" them do. We just don't have the same control over our "product" as many other workers do. Thirdly, the measurement process cannot be more burdensome than the job itself, however to really do it in ways that capture all the qualities you want in a teacher or doctor or whatever, it seems like it might have to be. Test scores are easy to measure, but don't tell the whole story, just as blood glucose levels or cholesterol levels or scores on a depression questionnaire are easy to measure but don't tell the whole story about what makes a good doctor. But the data is easy to get, so this is what is measured. It's like the old joke about the drunk guy looking for his keys under the streetlight, when he lost them 50 feet away. When asked why he was looking there, he replied "because that's where the light is."
I know teachers who evaluate their own efforts and work to improve their evaluation, but I've never seen a group/union/department adopt outcome-based standards with any accountability. I'm sure exceptions exist, but this needs to be a broad trend in education to improve teachers' public image, and, most importantly, students' educations.
*Not that I'm an education expert, but I know so much less about medical practice that I have no idea how much this applies to your field.