That information should be coming in the mail in mid-May, so just a week or so. You'll probably receive more when you get your report cards in the mail after school's over.
If your school does Tux-and-Drape shots, here's how it works:
Guys: The photographer provides the tuxedos. Expect to be at your appointment a while because you'll have to change. Wear a white undershirt. The photographer has a wide variety of white shirts and tuxedo jackets . . . and they're all split up the back to accomodate fellows of all sizes. Once you're dressed, they'll "close you up" with big fat plastic clothespins. You only have to look good from the waist up, so you'll likely be wearing shorts or jeans, but no one will know. Get a fresh haircut one week before your picture, shave immediately before leaving for your appointment, and don't forget your class ring -- sometimes the photographer does the fist-on-chin-thing, and your hand might show.
Girls: Again, the photographer provides, and expect to be a while. Wear a skimpy spaghetti-strap top (and you'll pull the straps down past your shoulders). The drape looks like a big black velvet beach towel with a little rusching in the middle. The photographer's assistant will wrap it around you, and it'll close up with velcro in the back. You can't walk around in it -- it'd fall right off (that's why I recommend the spaghetti-strap top). Practice at home with a towel and consider "how much" shoulder you want to expose. Attempts at being overly modest look . . . odd, but so do attempts at showing too much cleavage. It looks best sitting on top of your shoulders, pulled nice and tight -- trust the photographer's assistants; they do this all the time. Ladies' hands do not generally show in the pictures -- the drape prevents it. Because the drape is rather exposed at the neck, tan lines are frequently an issue for ladies -- with a few weeks' notice, perhaps you can plan ahead to avoid that problem. You might want to wear a favorite necklace (make it relatively short -- long wouldn't look good with the drape), though the photographer often provides a string of pearls. IF your school does pearls, consider earrings to match -- silver earrings with pearls are . . . odd. Do not wear a pink bow or something equally "clash-y" in your hair.