Each student has a big spoonful of cornstarch in a container and then added water, a bit at a time. They stirred the mixture with a Popsicle stick until it was just the right mix between a liquid and a solid. They were able to gather it up in their hands like a blob of play-dough like a solid but when they held it flat in their palm, it ran between their fingers like a liquid.
Steve Spangler has some amazing Science trick for kids and this one is covered too here. We even found a video online where the mixture was made so you could walk across it or sink in it if you stayed still. You can link to that one here.