I purchased these ice trays 2 for $1.00 from the Dollar Tree. Can you believe that Walmart wanted almost a buck-fifty per ice tray?! I knew that I could do better. The ice trays are a great way for your students to practice sorting. They can also be used purely as storage after being used on a magnetic surface, and if you write the numbers inside the bottom of the ice trays, your students will be able to easily clean up.