This is a simple experiment with a test tube, oil, water, food coloring and alka seltzer. Probably one you did back in preschool... But - let me tell you from first hand experience - "big kids" are not too BIG for this experiment!
This is our co-op class - made up of middle and high schoolers. They all enjoyed this demonstration, and we had the chance to discuss some high level science concepts as well. Concepts like density, diffusion, the chemical properties of carbon dioxide and the polarity of water can be observed, discussed and remembered! Not to mention the mesmerizing effect of watching the bubbles go up and down the tube that you never outgrow...
With a couple of household chemicals - we also taught them how to make some pretty cool "explosions" too! I promise you, we captured their attention - and they will not soon forget this lesson!