Would teachers or students get a better test score?

That depends entirely on what they were being tested on, and the individuals involved. If it were the subject of the class, then you would hope the teacher would score better than his or her students, but that isn't always the case, especially with adjunct professors hired to teach an unfamiliar subject three days (or less) before the class starts... which happens sometimes. Even when the teacher is a whiz, there could be a student that knows more, and just has to take the course to prove it. If it wasn't about the class, then it is up in the air depending on who is more familiar with the subject matter.