I like aeh's helpful perspective on this.
We have over the years also had the unfortunate experience of a handful of teachers who were determined to take DD down a peg or two, using whatever means came to hand.
Not giving "the" answer-- or going beyond it... or not being LITERAL enough (that is, stating "XXXX happened in 1648 because YYYY happened earlier that same year" rather than "XXXXX occurred late in 1648" or things like this.
It can be maddening, and can definitely lead to cynicism. Particularly if one catches whiffs of a teacher's personal bias sneaking into things. For example, my DD had one teacher in an AP course who docked her points for not mentioning in an essay (which was open-ended) that the New Deal made the economic collapse more severe and prolonged the period of unemployment.
Really not kidding about that one.
She had quite a stinker for biology in high school, as well.
