This is the best idea I never had.
My colleague, Tom Chan, asked me in the Math Office this morning, "Where are you guys at?"
I told him, "We're on volume of a pyramid."
"Me too!" He's usually a pretty cool cucumber, so this caught me by surprise. He said, "We're doing proof of the volume formula by Play-Doh. Wait here a minute."
He dashed out and came back within a minute with a fist-sized cube made of three different colors of Play-Doh.
"Each table gets three little tubs (so three colors) and they have to make three identical pyramids that fit together into a cube. Then they can move on and do the next piece."
I was dumbfounded. The best I'd been able to do for today was to produce tiny, helpful diagram handouts to fit into our INBs.
But I'm bookmarking this for myself for next year by blogging it, and by giving full credit.