Apparently acetone or any organic solvent work well to dissolve styrofoam also. https://sciencing.com/acetone-styrofoam-experiment-2768.html https://sciencing.

Apparently acetone or any organic solvent work well to dissolve styrofoam also. https://sciencing.com/acetone-styrofoam-experiment-2768.html https://sciencing.com/acetone-styrofoam-experiment-2768.html Though, that's probably not elementary school safe. It doesn't remove the Styrofoam though. The Styrofoam is broken down into long chains of molecules which remain in the solvent.