Building out a physical model was tough. We don't have anything to resemble molten rock in our classroom, and getting a whole bunch of putty (similar to molten rock) would be expensive. We settled on water and are cognizant of its limitations (but we're okay with that! We also realize that using any heat source available to us at school is a very small fraction of the amount of energy coming from the earth's core, but we're okay with that, too!
So using some tubs of water, some mugs of hot water under them, and some food coloring, we created this model of the core and mantle of the Earth!