I am am old school teacher and operate an Early Childhood Program. I have seen these kinds of stories for a long time.
I would first tell you to talk to his teacher. I would also request that he meet with the school counselor. If this an emotional issue (what if he is trying to stay out of middle school.) He probably is not even couscious of this impending major change and its ramifications, but feels something.
You may also be right with questioning his hormones. The growing up process seems to be moving down younger and younger. He may be over-whelmed with the stories that his friends are bragging (anything from girls to drugs) that he feels totally unprepared to deal with. The thought of leaving his school and teachers he knows could also be part of this puzzle. Talk to your pediatrition and see if he can make some suggestions. Talk to your minister and see if he has any repore with your son. Keep looking for some answer.
Remember there is no one answer. There are lots of directions that this could be going. I am sure that you are so frustrated and concerned for him. Try to keep up a positive relationship (talk about other issues besides school and problem areas.) He may not know why he is acting/feeling this way, and you need to keep options for conversation open, so that if he can verbalize his problems at some point, he will come to you.
Know that every parent faces these issues at one time or another (even if they won't admit it!!). Try not to yell at him about this, if he isn't making changes, send him to whatever discipline works (grounding, chores, taking special items of importance). Make sure that he understands that you are having to discipline him because he "is asking for it". Do not take the blame for being mean, so out of it, or whatever. Try to remain calm, which is so hard, as this such an emotionally charged situation.
Be prepared that this is not going away over-night, but in little bits and pieces. Try to keep track when one behavior changes, so that you can point to his success.
Good luck. I don't have all of these answers, but understand how difficult it is when your good kid changes over-night.
J. Loftus
Willow Woods Child
Development Center