In USA, I guess. In my town in Sweden, it's a very VERY formal thing we practice dancing for for months together with our chosen partner before the event. We start the dance practices every sunday or wednesday (we're often hungover) in January or so, and the dance is in June. The big day, a prom commitée, traditionally composed of some high school students, rent the big sports arena in the city and we perform a long dance to different songs, in formations and sorted by dress colors and whatnot. After that, we go in fancy cars to the biggest park in town to eat strawberries and have champagne, it's wonderful, and then we sort of dance in a long line into town where all hundreds of prom goers have a huge, fancy dinner party. During which everyone gets madly drunk and blissfully crazy. And then it's a party, at every club downtown you'll see fancy dresses. It's wonderful. When you are one of them. When you get older, it's just silly, haha. And memories.
:)