Nice intro lab to get students started at the beginning of the year. Students don't realize until the end that they have made play dough. Unknown substance is just unsweetened powdered drink mix. Play dough can be kept in class for further use or students can keep it. I like to allow students to roll progressively smaller balls out of the play dough to reinforce the metric system (divide into ten balls, then take 1 ball and divide it into ten and so on).