I think any kind writing is writing, but we just need put it in order. A paper can be graded C because that paper might not have followed all the rules. This means punctuation, grammar, verbs, tenses and others. In a C grade paper maybe there are fragments. Fragments can make a paper miss its attraction. For example, 

     - The requirements before registering for classes.- Fragment

     - I have lunch yesterday, but not today. - Here the verb tense is the problem.

These types of mistakes can lower the grade of the paper. Another reason is the paper may not have connected its story. It needs to be in order and organized. 

     When we are grading an A paper we will see how well it was organized. In that paper we can find college level vocabulary, followed the rules of writing and it is attracting the reader. For example, sentences are very clear in the paper; the requirements are take placement test before registering your fall classes.

     -I had lunch yesterday, but not today.

 In A paper there should be a grabbing point and must go through its story until to the end of the paper. Sometimes the paper has to convince the reader. When the paper is attracting and convincing the reader it is an A paper.