Understanding the Phases of the Moon
Object: to understand why the moon goes from new to full phases
Method: Place two balls and a flashlight on a table. The balls stand for the earth-moon system, while the flashlight represents the sun. Shine the light on the 'moon' ball as it is slowly rolled around the 'earth' ball. When the moon ball is between the sun and the earth, the light will only shine on the 'unseeable' side of the moon. This is the 'new moon' phase. When the moon is at right angles to the sun-earth axis, a first quarter moon exists (while it is called 'first quarter', the moon actually appears half lit). When the moon is behind the earth, a full moon can be seen. Note that with this model you can also demonstrate eclipses.
School Instruction: Once the students understand the earth-moon system , and how it is lit by the sun, have them demonstrate an eclipse. For a solar eclipse, the moon must be between the sun and the earth. For a lunar eclipse, the earth must be between the sun and the moon. Ask why eclipses don't occur every day (they actually do in space, but are not always exactly aligned to occur on earth!).