I experienced a bit of this myself (teachers being against me). And other people for that matter... my philosophy on that.. I would make it my goal to prove them wrong and I would work as hard as I could to prove them wrong (that I could do something and succeed... and I have in many ways).
I think if you let people get you down (teachers, other students, whatever) then, yes, you won't succeed, but if you tell yourself that you are better than they think, and take on the "I'm going to prove you wrong" attitude like I did, I think you will surprise yourself and them as well. I know it sounds eaiser than it may actually be, but once you do, the feeling that you "beat" them is a good feeling.
I had a few professors that didn't think I would get very far, and I felt the same way myself, that I would just settle for average, but I worked hard, even against other people's advice (which at the time, some of it was useful, but some of it probably would have slowed me down had it followed it) and from what I can see in my life, it's paid off. Both figuratively and literally.
Point being, people will tell you you can't do things. Prove them wrong. But I will ay this though, it may not be easy and it may be an uphill battle. Mine was, but if you keep a goal in mind, you should be able to get through whatever despite what others may tell you.
And for the part about "disappearing." Don't do it. It's not worth it. I think you just have a lot going on and a lot of external stress causing you to think that way. I know that I've had times where I just wanted to die, but am glad that it never came to that. I've considered it (a long time ago when I was younger--younger than you are now), but look at the positive things you have to live for. Me personally, I couldn't see myself ending my own life... Heck I can't even build up enough strenght to hit someone if I needed to--no matter how mad I get.
When I was in HS, I didn't get the best grades, I didn't participate in the groups or clubs, I didn't date, or anything. I thought I had hit rock bottom in life. HS sucked for me for the most part. I just floated on to get through with the bare minimumum I needed to finish. Then I got to college, and things really turned around for me. I actually enjoyed college life, did a lot better in classes and was able to successfuly complete a 4 year degree with a high GPA. And all along people (mainly at work where I used to work) would tell me that I'd be stuck there (at work) for life, not going anywhere. I proved them wrong, and quit my job in favor of a better (higher paying) one. I don't feel sorry for my fellow co-workers. I told them I wasn't staying there for life, and I did something about it. I didn't let them dictate or influence me. I kept my goals in sight and worked toward them each day.
(In case you haven't noticed, the "prove they're wrong" is sort of a game/motto I use for myself to boost myself and get things accomplished and feel good about it.)
You have to ignore the teachers and bullies and do your own thing. Everyone can succeed if they try.