High School Prom Dances?

This is going to be my first year (because I'm a junior now), and I think I've gotten the basic concept of what a prom is really like from my friends, but I have a question about the kinds of dances. I'm pretty sure it depends on what school you go to, but is there usually themes? are there formal dances or is it just plain ol' get wild partying dance? or maybe a bit of both? anything would help :)