What would go into determining which of the three ratings a teacher received? Obviously we know who is doing a good job but how do we prove what we know? I think it would end up becoming some type of rubric that would lead us down the path that we are on now.
Honestly, a straight up vote by selected teachers and administrators with no justification required would probably be most effective but also the least likely to happen.
I'll give a real example of a teacher that is poor and hard to get rid of. She meets all professional expectations as far as coming to work on time and taking care of all of her before and after school duties. She plans with her team so her plans meet expectations. She doesn't do a good job teaching math and science but does an average job with language. Her behavior management is average at best. Since everybody knows she doesn't teach key subjects well, she doesn't get as many of the behavior problems or really low kids. Her test scores come out about like everybody else, maybe slightly lower. We all know that she would fail given harder students.
Other than just by knowing what is going on, how do you fire her? You could obviously stop giving her easier kids but you put your school at risk of dropping in accountability rankings and no principal in their right mind would do that. Once again, what we know is easy. It's being able to prove it that is the challenge.
Also there are teachers worse than this that I have seen but they have all been fired.