This is an easy hands-on experiment to do when introducing the Scientific Method, during life science instruction and/or when teaching hygiene.
When my class does this experiment, I take pictures of the before (dirty hands) and after (one hand washed with water and the other with soap and water). I display the pictures with the experiment write-up on my science bulletin board.
It's dirty but lots of fun!
I have included a 4th page so that you can input your own number results and graph.