I am the kind of dude that would go to your seventh grade class and sit at the back of the classroom and stare at all your butts.
The secret to writing sound effects is having a room you can be alone in, trying to make the sounds yourself, and seeing what comes out. It's similar to if you're writing a character talking with their mouth full: the only way I know to transcribe that is to stuff my fist in my mouth and write down what sounds I make when I try to talk.