The Wise Man and the Foolish Man
 

When I taught this, I built two small houses out of cardboard. I found a pretty nice sized rock that the house fit over the top of. Then I got a bunch of sand and the put the sand and the rock in a casserole dish.  I told them about the foundations of homes and how strong they are, etc. I then poured water over both houses and the house on the sand washed away, tipped over, etc. The children loved it. (Idea by Julie McKenna)