My wife is a grade school teacher.

She did something like your experiment with the kids, but it was 2-fold:
a) to show them how well (or badly) they wash their hands
b) to show them how they spread germs

Part a:
1) Got some clear 'goop' that you can only see under a blacklight, and had them do the hand slathering thing
2) Had them to wash their hands as BEST as they could
3) Had them look at their hands after washing, under a blacklight, to show them what they missed

Part b:
1) At the end of the day,
2) she shut off the lights
3) Went around the room with the blacklight to show them everything they touched (i.e., the 'germs' they could have spread)

Quite a 'revealing' exercise.