Why is my Dad so grade-struck?

Grades, grades, grades. That's all I've been getting from my Dad. He doesn't even understand how hard my work is in school. My homework is piling every single day and when my Dad sees it, he gives a 20 minute speech about his goal to get rid of me from the house. During these lectures, he always criticizes me on how stupid I am, things that are hurtful to me but aren't true. And what happens when I finish the quarter with an 89? Everything is taken away from me, leaving me with nothing, and his lectures are thrown at me. Seriously...a B! That's just passing and still he gets wild?! He says that he had straight As in his school ALL THE TIME and never did anything bad. He says that fact gives him the right to patronize me. And also he claims that I FOOLED him? What did I do? I just got a B that's all. And now that I'm going to end this quarter with a B, another series of consequences. I want to show him that mistakes happen but I don't want to upset him. Please help me.