When I was in the eighth grade my science teacher bumped up my overall grade by 3% in the middle of the term because I "actively participated" in one session.
I'm not sure I agree with other posters in this thread, if they're suggesting you are indeed falling short on participation; I believe that from what you have explained... you are participating and you are being treated unfairly.
I can't accept that the 'burden is truly yours' to demonstrate your participation; if the teacher fails to bring it out of you then it is certainly a failure on part of the teacher. They are supposed to lead the way and show you what is required.
The argument "have you ever had to teach fifty students" is a bullshit argument. If you are in Junior High the answer is clearly no, plus... it's not impossible to conceive how difficult it would truly be, which is not very in this case. In the absence of further details regarding your classmates, the state of the nation, the condition of the school, the curriculum, etc ... all extraneous variables notwithstanding, your teacher is still obligated to grade you on your personal participation in class, therefore your teacher is obligated to enable you to participate properly, even if it means treating you different from the average student. Some people can not be normalized and at your age they should certainly not be punished for it.