There are certain teachers in high school who, when grading an opinion piece, will be extremely biased in grading because your paper reflects an opinion differing from their own. This, of course, is complete crap.
I've learned the hard way that if you try to talk to them about your grade, they will yell at you in front of the class and they will act like a child. So what do you do? Make your paper damn awesome. Give them no reason to give you less than you deserve.
If you get another ridiculous grade, stand up for yourself. Never let them win. Never wave it off, because it's your grade. Do not let them convince you that it's unimportant because it is your grade!
If you're ever in this position, make sure to WIN! Good luck.