I decided to bring petri dishes into the classroom for the children to experiment with. I wanted to give more visibility to the invisible world of germs (and distract them from wanting to study animals for the millions year in a row for science). Turns out they LOVE the dishes and are anxious to test all sorts of things.
To kick things off and get the children used to using the materials and thinking carefully through the experiment process, I started by asking them to help plan an experiment that would help us determine if hand washing really works.
Some initial considerations the children thought of to make our experiment more reliable were
Needing a comparison-- we need to know what the hand was like before washing in order to know if washing really made any difference (Lila told us that was called a control test, which she had seen on Myth Busters)
The regular hand and the clean hand needed to be from the same person. Different people have different germs, so it wouldn't be a fair comparison. You need to know what THAT person's hand was like before and what THAT person's hand was like afterwards.
We would want to test the regular hand and the washed had close together to limit exposure to extra germs in between.
We would need to wash for 20 seconds (the recommended hand washing time)
The test subject did not touch the faucet, soap dispenser, doors etc. to avoid extra contamination (though later it was questioned if these were necessary since in real life you would actually touch all of these things when washing your hands).
We tested and waited for about a week for things to start growing in our dish. It was very fun to watch the children come back from the long weekend to see the newly visible growth.
"If you look close, you can see little hairs!"
"They look like grey dandelions!"
"Wait! The clean is dirtier than the dirty!!!!!"
See for yourself! The results are surprising!
* Note: The original science chapter I was reading in the
Best Practices book shared this experiment. The author said he started off every year with this test and that the results were almost always this way with the washed had growing more than the dirty hand. I wasn't sure our test would be so surprising, but it turned out to fit with the author's experience. The discrepant event has the children completely baffled; it has them RIGHT where I want them to be. Now they will get to put their brains to the test to solve the mystery. (P.S. I did run the experiment exactly as they had planned. No foul play by the teacher to trick them)
How can that be? Why does everyone want us to wash our hands? Why do doctors wash their hands before surgery? Should we stop washing our hands? Did something go wrong?
"I think you must have mixed up the dishes!"
"You probably accidentally used the same swab twice."
"I think it matters how long you wash."
"Maybe the soap is dirty. I don't think the soap is sterile."
"What if waving her hands in the air after she washed actually gathered more germs on her hands?"
"Maybe the dirt in the dirty dish keeps the germs from reaching the agar, so it can't grow as well."
Some children seem convinced that they should just never wash their hands again. Others feel like there is a problem and we need to get to the bottom of it.
"We may never know."
"We should leave this to the scientists."
"I think we are going to have to make a list of things we think could have gone wrong and test to rule each thing out."
