Testing throughout the year and measuring performance based on that seems like a bad idea to me. When I was in school the only important tests were at the end of the year (the tests everyone in the country would take at the same time: GCSE, AS Level, A2 Level etc.). Therefore I only worked hard for them and put little effort into other tests throughout the year as there were no long-term consequences for doing badly. So the only good way to judge a teacher based on performance would be to look at the final exam results and to ignore the results throughout the year.
