Maybe to really demonstrate the idea of a figure that tessellates is best understood by one that does not.
Hexagons are the best figure to show symmetry by rotation.
I coordinate an enrichment program which brings me to three elementary schools. I work along side classroom teachers. I recently lead two workshops with fourth graders using your lesson plans. The kids loved them. A smaller group from these classes came to the HyperCard workshops the next week and the week after.