This is pretty much why you have to have standardized tests. Subpar teachers like this one. You couldn't possibly trust someone like that to make any sort of valid evaluation of her students.
Also a lot of the motivation of the teacher who was annoyed with my parents was that I was causing problems in tests due to being interested in stuff well outside the domain of what would be taught in class.
Set tests largely test how good you are at those set tests, but most problems you will encounter in the real world are unbounded by a curriculum and the ability to recall stuff you have very recently read, while useful, is not a particularly good measure of wider ability.