Paper Airplane Contest

Give your participants supplies to make their airplanes; paper, markers, scissors. Let the kids who already know how to make one make theirs while you lead a tutorial for the kids who don't. Demonstrate how you make your airplane and help the younger kids get clean folds. Have them decorate their planes.

You can introduce things like tape and paperclips for them to use, too. If their airplane tends to dive to the ground, the front of their plane may be too heavy and they could try adding a paperclip to the back. If it tends curve upward it could use some weight on the front. If it curves to either side it's wings may be bent or it is asymmetric.

Let them practice flying a bit. Then have a flight contest. You can have them line up and all fly their planes at once. To make the activity last longer you can have them go one at a time; have them each fly their planes to see who's goes farthest, then go through the line once or twice more to give them another chance. Maybe ask the winner to show everyone else how they made or modified their plane.