I had all of the supplies to make marble runs as part of a school-aged Engineering Challenge, and I thought my younger Science Storytime preschool friends would also like to experiment with the supplies. Unsurprisingly, I was correct.
To begin we talked about hills and rollercoasters, trying to elicit from the children their life experiences with how things roll. They were eager to let me know that balls roll down a hill, and that they do not roll up a hill. There was some excitement when I used a marble run to show that if enough momentum can be built up, the marble will roll uphill. I demonstrated this several times, with lots of thinking out loud and experimenting with how steep the angle of the run needed to be before the ball would go over a small hump, to make sure that the students understood 
the basic idea. Then I handed out marbles and pipe foam that had been cut in half, along with our ever-present painter’s tape, and let the children experiment on their own.
As usual, the range of exploration was wide. Some of the younger children were happily entertained for a very long time simply rolling marbles down a track. A few of the parents wanted to move on to more complicated designs. I wish that I had made it more clear that, especially for young preschoolers, just interacting with the materials is a learning experience all in itself. Rolling the ball down the track repeatedly is building up a schema of how the world works that will be helpful to that child later, even if it’s not the sort of “experimenting” that we’d pictured beforehand.
Some of the children added the toys that were already in our playroom to their marble runs. Of particular interest were the buckets we keep smaller toys in. Several children wanted to set their marble runs up so that the marbles would land in the bucket. (I wish I’d thought of that ahead of time, because once this idea caught on it definitely made containing the marbles rolling all over the floor much easier.) Other children used the buckets as ramps in their building process. Another child spent a lot of time with a school bus, first figuring out how to get the marble to roll through the bus (harder than it sounds when you’re quite small and the materials barely fit) and then using it as a base for a loop-the-loop that was her own self-initiated challenge.
