On good and bad teachers -- what's the standard? I've been in a number of discussions about teaching excellence. I was even on a committee once to establish a teaching award. I've never found agreement on what constitutes a good teacher. Not surprising, since first you'd have to agree on the purpose of education, and that's not going to happen. Instead, the discussions always end with some version of "Everybody knows who the good teachers are." I have a problem being everybody.
I have yet to find anyone who could really balance out all the different teaching strengths and weaknesses, including what kinds of students they reach, what strengths they help the students with, how much trouble they cause the administration (hint -- social status of the parents is not excluded from consideration), and so on. So I find any merit system an exercise in delusion. However, my experiences with bad doctors and dentists leave me believing that there is a level of incompetence and professional neglect that colleagues have a responsibility to address.