I read it to be that the teacher took off points for grammar errors that were not errors...
We believe that any grade below a 90 is a failing grade in our house. When my DS got a B- on his paper, yes, I wanted to find out why. On top of his low grade, I had proof-read his paper and knew that there were no grammatical errors in it. I needed to find out why he got such a low grade.
The teacher was also shocked that I was not happy with that grade. I guess we aim high with our children and their grades. If you don't aim high, you can't achieve a lofty goal. My kids want to go to a prep HS. They won't make it into that school without earning high marks in MS. It is not something that my DH and I have forced on them. They want to go to the prep school and they want to be successful in school.
Moving on to the subject of READING COMPREHENSION, why don't you look at my post and see who I was replying to.
And FYI: I think a 7th grader should be capable of asking a teacher WHY they received a certain grade.
He did try to talk to the teacher, but she talked above him and couldn't give him any reasons why she graded the paper as she did. Remember, she didn't have a rubrik for us to review, either.
After our meeting, the only thing that changed was that she knew I was capable of helping my DS to write well and she never graded him that poorly again... even when he turned in the paper and I hadn't read it first.
I truly believe that it was his subject matter that caused the grade. As I said before, he wrote about his uncle whom people either love or hate. He learned his lesson and will not be writing about his uncle again.
OP, sorry that this wound up affecting your thread. I loved the suggestion to have your child correct the teacher's note as a homework assignment.

Even though I have a lot of guts when dealing with teachers, even I wouldn't follow through on that suggestion. It did make me lol, though.