In the Mystery Science Unit, Spaceship Earth, students learn about the phases of the moon and what causes them. Here they used a flashlight to represent the sun, a styrofoam ball as the moon, and a skewer to hold it up. Rotating around demonstrating the moon's orbit around the earth, students got a great visual of why we only see parts of the moon during each month.
You can do this at home with a similar ball or even an orange!