Why do i act clueless?

I am 12 and i go to a small private school and there are only about 35 kids in my grade. There is this guy who i almost have every single class with and i talk to him a lot. I don't really have a crush on him but whenever i talk to him i find myself acting clueless and pretending to be dumb, even though i am practically a perfect student. I don't know why I'm doing it, i don't mean to. Any advice?