In response to Willingham's comments about evaluating teachers, these are my thoughts:

I particularly agree with Willingham's point about comparing Teacher A (who has low-performing students) to Teacher B (who has high-performing students). As a former teacher of both honors students and students with learning and behavior difficulties, I agree that it is not equally easy to achieve gains for each type of student.

As an honors teacher, I had students who came to class on time and prepared, paid attention to the lessons, and completed classwork and homework assignments (at least most of the time!). When I taught low-performing students (some of whom had been diagnosed with specific learning or emotional disabilities), it was difficult to make progress (although it was very heartening when progress was made). Students often did not come to class (or came late or unprepared - i.e., with no materials, did not have the homework from the night before). Students did not always pay attention to the lessons, and were more prone to chatting with friends or trying to get the hall pass than honors students. All in all, it's hard to come up with a fair way to evaluate all teachers, given the wide variety of students and subject matter handled by each teacher.