How to get a 5th-grade classroom to jump up and down like idiots

This is a little joke I played on my 5th grade class this past year. It was 4:30 in the morning two months ago that I woke up with a fiendishly clever idea. This idea was so brilliant that I couldn’t help but begin work and keep going nearly until school was nearly ready to begin at 8:20. I wanted it to be awesome. It was April Fool’s Day two months ago, and I decided to play a little prank on my class. You see, I’ve never played a practical joke on my whole class before (at least that I can remember)