Additional Information: Helpful or Making Excuses?

So I was considering using the section of the Common App to explain a few of the reasons my grades dipped junior year. If I were to use it, I would explain that one of the main reasons was due to coming down with the flu, and then later on in the year, pneumonia which resulted in a hospital stay, and over 10 absences resulting in my grades all being lowered by 10 points (school policy). Not only that, but my AP English teacher bullying me for the entire year, sabotaging my grades (not giving me the change to make up work, saying that it “wasn’t his problem” and then giving me zeros or giving me 60s for work that other students received an 80 for), and then, after I brought it to the attention of the school, my grades in participation suddenly lowered (I saw them originally as in the 80s, and then on the last day they went to 70s, this was before the 10 point reduction) and I was told by the school there was nothing that could be done. I was forced to take summer school, in which I got an 86, and I even got a 4 on the AP exam, showing I did know the material quite well. Would my explaining this in additional information be just making excuses, or would this be helpful to schools I apply to in explaining the inconsistencies in failing the AP course, but receiving a 4 on the exam?

I think a partial explanation would be okay but some of what you stated will come off like making excuses.

This seems like a valid point to convey, that may be best when written by your guidance counselor as part of their file/letter:

I would leave out coming down with the flu (which, honestly, happens to almost all students). Saying teachers were bullying you or not giving you the grades you think you deserve will sound like excuses. If you have provable examples of unfair grading or other actions against state/school policy then try to resolve that with the school/district. For most schools if you have excused absences the teachers are obligated to provide opportunities for making up work. If this is a policy that wasn’t followed then you should address that with the teacher/school although it may be too late now. Stating it on your college application will seem like excuses.

It may be necessary to involve your parents with the school district. Sometimes it’s just the case that their voices are more powerful than yours.

Yep. Pneumonia is the only non-excusey item in your post.