Well yeah, if you know more than the teacher themselves, their ignorance will cause your scores to drop because they aren't equipped for the job in the first place, I've seen those Japanese English classes, they'll teach you gramatically incorrect english sentences and they can't pronounce anything correctly. Though it could just be she is incompetent at english. Or it could be that its more of a teaching English through Japanese like a translation class instead of a language class, for example imagine this question.
Japanese question
Their
They're
There
An expert English speaker wouldn't know the answer because the question is in Japanese.