This rubber band-powered car is a great example of a project an elementary student might complete in school. The prompt for the assignment could be to design a car powered only by one rubber band, that would move a certain distance when the rubber band is pulled tense and let go.
Print Body in True Red and all other parts in True Black.
Put the Small Axel through the front holes of the Body, then attach the Small Wheel to the end of the axel. Do the same for the Large Axel and Large Wheel in the back holes of the body.
To power the car, slip a rubber band over the T shape in the front of the car's body, and wrap it around the back axel, slipping the end onto the notch to begin. Pull the car back to wrap the rubber band around the axel multiple times, then let go to power the car forward.