On one hand, a poor measurement of teaching performance do more harm than good. However, it is also true that human judgement of student performance can easily

On one hand, a poor measurement of teaching performance do more harm than good. However, it is also true that human judgement of student performance can easily be skewed in various ways. So, the solution is to find some kind of measurement that accurately reflect somewhat student progress. This way, teachers can reliably test education experiments. Of course, the larger problem is probably the teachers' possible resistance to the scientific method and poor training in devising experiments.