What is appropriate to wear to high school graduation?

A bunch of my friends are graduating this year (I'm still only a sophomore) and so a few friends and I are planning to go to the graduation. What am I suppose to wear? I've been to two, both of which I had people put me in a dress or skirt and I seemed overdressed. And I'm not really keen on wearing a skirt or dress, but is that what you're suppose to wear...?