He put in my grade as a zero for a lab writeup and it dropped my grade badly. How would I go about confronting him about this? Like what should I say? Again, I believe it was a mistake on his part because I did turn it in. I don’t want to sound like I’m accusing him of anything. So what should I say?
“Why’d I get a zero on the lab write up?”
Then proceed from there
“Hi, Mr. So-and-so. I was checking my grade the other day, and I saw that I got a zero for such-and-such lab assignment. Is there a time when we could discuss this assignment? I thought I was going to do good on it. Could I see the assignment so I know what I did wrong, and could we talk about why I got a zero?”
If he didn’t get the assignment (for whatever reason), he’ll tell you, and you can work out what to do since you thought he did turn in the assignment. If the zero was an accident, he’ll tell you and fix it. If you did something wrong and that was why you got a zero, he’ll tell you and you can make sure you don’t do it again.
Just ask him why you have a zero on the lab
I would ask politely. Say you are sure you turned that lab in, but you see a zero in the grade. Could be an honest mistake. If you have the lab paper, certainly bring it. Other possible explanations: you forgot to put your name on it. Or D2 had a teacher that wanted assignments at the start of class. D2 came in a couple minutes late one day, and he gave her a zero because she did not turn it in on the hour.
Thanks guys. I’ll ask him about it tomorrow. He’s an understanding guy so I think he won’t be mad.
I don’t think a teacher should ever be mad if you ask politely and in good faith about a grade that may have been posted incorrectly.
Don’t confront-- inquire.
“Mr. Smith, I noticed that I received a zero on the lab. I know I turned it in-- could you check on that grade? Thanks.”
Teachers, like everyone else, make occasional mistakes. And it’s particularly hard at the start of the year when we’re trying to learn hundreds of new names. As long as you’re not confrontational it shouldn’t be an issue.
A really skilled student will make an “appointment”, more or less formal depending on circumstances, to ask the teacher some questions and “review their progress in the course”. That way, the teacher has the opportunity to either bring the gradebook up to date in advance or to “discover” the discrepancy at the same time as the student.
It’s done guys. He misplaced the paper. 
Thanks for all your advice.