Where I go to school, the second day before break we have a cookie station set up in the lunchroom and play Christmas music over the intercom between classes.
The last day before break, we don't have classes and everyone packs into the theatre. The seniors bring confetti, toilet paper, balloons, air horns, remote controlled blimps, etc. and destroy the place while other students and teachers perform on stage.
What's your school's Chrishmas tradition?