Buy a frozen brick (or more) of ladybugs from a seed catalogue and throw them in inconspicuous spots all over the school. Soon, the beetles will be so thick they will have to close down.
Or, take a hammer and a punch, and puch a hole in the bottom of all of the porcelain urinals of a top floor restroom.
Zip tie the floats down on the toilets, and plug the drain. That way water will come at an alarming rate out of the top of the toilet.
Get a little cork and drill a hole through it, and stick it in the drinking fountain where the water comes out.