Why does everyone call me stupid at school?

I'm thirteen and I consider myself an upstanding student, I get all a's, minimal spelling or grammatical errors and am taking college prep cles but still my friends continue to call me dumb even when i get better grades then them! Whenever I make the slightest slip of the tounge they take the opportunity to pounce. My ex boyfriend teases me and calls me "dumb as a bag of rocks" and my current boyfriend calls me dumb but says he "doesn't mind". It's really starting to take a toll on my self confidence. I have a very bubbly and ter brained personality and maybe that's part of the reason, But I'm really intrested in learning how I can prove to them I'm not as airheaded as they percive me to be. 10 points for best answer!