The sixth graders did a class project where they used the scientific method to hypothesize about the things that make a plane fly the best. They then designed and built their own 'planes' with a partner to test their hypothesis.
The only control for the project was that all teams had to use a 2-liter bottle for their fuselage. We learned about stabilizers such as elevators, rudders, and ailerons. We also learned about the position and size of wings.
Blueprints were drawn to scale, and construction was based on their measures. After a test flight or two, students determined if more ailerons were needed or if trim (weights) were necessary to make the planes go further.