The problem with trying to identify "high performing" and "low performing" teachers is that so much of the rating process is subjective. We've all heard the comment that, if a teacher has a classroom of kids without family support, enough sleep, or a safe place to do homework they're considerably less likely to have a classroom that excels on standardized tests than a teacher in a school where those things are de rigeur...but the converse is also true. A teacher who refuses to individuate teaching for gifted kids, who doesn't follow the deaf kid's IEP, who relies on endless worksheets instead of making class interesting can still be considered "highly effective" simply because she has a preponderance of bright kids who test well in her class.
Likewise, one could rely on student (or parent) evaluations of the teacher, but that has its limits, too, given the politics of the average third grade classroom.
I won't get sucked into a discussion of the usefulness of unions, because that's a polarizing discussion with only very tangential bearing on gifted education. But I'd love to know what others think is a good method (at least in part observable, measurable, and not subject to circumstances) to define "highly effective".
