the above suggestions are great.
when i feel i am about to slip into an anxiety attack i don't let myself. and by this i mean i do not let myself think about having an anxiety attack as soon as i feel it coming on, even when i feel my heart pounding and i can't breath. i start to focus all of my thoughts to the stitching on my shoe, for example. mentally focus on something else (ANYTHING) and do not let your thoughts head toward the path of an anxiety attack. all the while take deep, calm breaths. "convince" yourself that you are relaxed even if you don't really feel it. you will get better at it the more you do it. i am 28 and still have to do this from time to time.
if people are really giving you that hard of a time in 12th grade, first, i think you should tell them (as hard as it is) to stop acting immature and to grow up. if they persist you should talk to a school counselor. tell them these people are distracting you from your studies and causing problems. you shouldn't have to put up with that shit. you don't deserve it. at the same time, don't feel too victimy about it. it's nothing personal. these bunch of dolts probably pick on other people just the same way they single you out. and they only single you out because that is THEIR weakness, that is their way of coping with THEIR insecurities. all the shit they are talking reflects poorly on them, not you. so please don't take anything they say to heart. (easier said than done, i know, but i got your back. team benatom!)