Do a proportional map of the solar system. Start with the sun the size of a golf ball. Calculate the size of the earth and the other planets as a proportion and make them out of paper mache. (The earth will be like the size of a BB.) Then calculate the distance from the sun to the planets, pace it off on the school grounds, and place the model planets in their proper places. This really shows kids how much space there is between the planets, how far apart the planets are and how tiny the Earth is in the solar system.