Decorating A High School Dance With A Winter Theme?

Just off the top of my head I would suggest cutting out huge snowflakes out of cardboard you can wrap them in foil to make them silver, or paint them white and add glitter. Use a lot of winter colored Christmas lights like blue sparkling lights and white or clear sparkling lights. You can use cotton batting for fake snow and place lights underneath or around for borders. A fun thing to do is a balloon and confetti drop which is basically a net with a pull cord it holds like 100 balloons or more up to thousands depending on what size you get but it goes on the ceiling and holds all the balloons until the pull cord is pulled like during the last song or whenever you decide then it releases all the balloons at once.

I get a lot of my ideas off pintrest, you might get some good ideas there. Also look into how to do balloon arches. They are fairly simple and a great way to fill empty space with classy looking decoration. Good luck!