School dances are usually all the same: The girls dance in a circle while the boys stand around, and the teachers and chaperons are just trying to make sure nothing inappropriate goes on. However, a school dance can be fun for everyone if you liven things up with some planned or themed activities.
At the beginning of the event, give the students dance lessons -- it could be square dancing, ballroom dancing, swing dancing or the Electric Slide. Choose a couple of teachers with decent rhythm (if you have a dance team, the coach is a perfect choice!) to be the demonstration couple, and another to call out instructions. The point is to have fun with it, though, not to make it like gym class.
Hold a Dance-Off
Have a dance-off. Let the kids all participate at the same time (think "Grease"), and choose a winner at the end, or let them come up on the gym stage or a set-aside area to dance for judges and spectators (think "Dancing with the Stars") while everyone else who wants to is out on the dance floor. And let the kids express themselves in their own style--they don't have to be limited to ballroom or traditional dancing styles.
Even the shyest pre-teens will get out there and boogie--if you can manage to make the focus something other than them. Transform some traditional party games into dance activities. For example, play musical dancers instead of musical chairs and everyone has to hold completely still when the music stops. Turn "Simon Says" into a dance routine.
Try a completely themed dance--for a disco theme give prizes for the best 70's costumes, play only disco music, and teach the kids "The Hustle". Throw a Hawaiian luau, teach a hula dance and serve sodas with little umbrellas. Or have a theme based on the nearest holiday--Halloween can get really fun!
Make It an Event
Consider making your dance more than just a dance by bringing in a magician, inflatables, arcade games and food. Then, it becomes an event that draws more students and everyone can have a good time, even if they don't dance the whole evening.
Most pre-teens and teens love karaoke. And you can add a little variety to your school dance by hiring a DJ with a karaoke machine and a willingness to work the kids' performances into his set.