How to survive seventh grade...?

OK, so I am entering seventh grade. This is my second year in middle school, and here is the problem: we have 3 teachers. The three teachers all teach 2 different subjects, and of course my homeroom teacher this year teaches my worst two subjects- math and science. She also is REALLY mean. She is usually unfair and hardly ever listens. One time my friend was getting up to get a Kleenex and we were grading a test and she got in big trouble becuz the teacher thought she was cheating and wouldnt listen to my friend wen she tried to explain. i've told my parents and other teachers and principal and they dont help at all. plz help me- wat should i do?? thanks ahead of time:):