There is also a lot of bias in this though. I have an interesting anecdote from this, one I'm not so proud of... For the first half of my writing 101 class I got a B-/C+ on every essay I wrote ~3-4. Then I took my girlfriends at the time "creative writing"/poem or whatever the assignment was and my teacher went bonkers about it thought it was better than sliced bread, tried to get me to take a creative writing class (which I milked and was like yaa i'll think about it). I wrote every paper after that and consistently got 95+ on them. Interestingly in the last paper one notable comment from her was "Your content is brilliant! your analysis of the book and your thoughts are the subject are amazing! however be careful with your sentence structure and grammer it detracts from the paper" I got a 97 on this and I put basically the same effort on this paper as I did in the beginning.

This is simple human bias if you expect something to be good it will be good, and has to do with how your teacher feels about you.