UPDATE:

He came up very upset and wanting to talk to me about the unfair thing that happened at school today. He added some information I hadn't hear - he also got points taken off of an assignment in his social studies class, since the assignment is to follow the laws of chivalry (which they're studying) at school and at home. Since his essay wasn't "chivalrous", he lost points on that assignment as well.

His reasoning for why he was upset:

The assignment did not ask for three positive things about one of the stories. It asked his opinion and why he had that opinion, and he did exactly that. He said if he liked the story because it was the shortest, how should he know he was supposed to lie and say something the teacher would like better?

He also did not understand why he could not use the words hate or sucked in his essay. He said he's heard the teacher use them, heard other teachers use them, and hears them all the time at school.

And so I tried to explain the difference between casual conversations and written essays and how some things aren't appropriate in one setting that are okay in another.

His response? Then can somebody please give me a list of what is not ok to write? How in the world am I supposed to know?