I think you should do as those above says: Keep it to yourself until someone has earned your trust and you know you can tell them.
I'm 14 years old, I've got three friends my age and the rest are at least two years older than me. I've dealt with a lot of immature bullshit, and twice it didn't end until it got really bad and they could see themselves, not only hear the words from me, that "oh hey maybe this is no good". Both those times were buddies who had figured out that I get really, really scared if someone frightens me from behind with touch. One of them would always frighten me by grabbing around my wait (shivering just thinking about it), he didn't stop doing it until I actually punched back and he collapsed on the floor and had to sit getting the air back in his lungs for the rest of recess. The other quit his crap when he triggered an anxiety attack during lunch break and at one point they couldn't get anything out of me because I was way too dissociated to hear what they said or even see them clear.
Some people need to learn it the "hard" way. If they are that kind of people, they probably shouldn't know about your story, unless you're 100% sure it'll make them more understanding.
If you can find one classmate who is capable of somehow getting all of it to understand that this and that are things you do not want to discuss at all, and this and that are things people should never, ever do to you, that might be good enough, because then this one classmate can back you up. One of my friends my age knows about my PTSD and most of my life, I guess he's the one who knows the most about me. He can help make others stop triggering, without telling why they can't talk about that/do that. He's just got a more confident way of speaking and people take him seriously, more seriously than a freaked out wreck screaming "DON'T. DO. THAT." for the zillionth time.