After thinking about it I think some other posters are correct.
Designing a plane and building from scratch is quite alot and likely too much to ask of an average high school student.
Building a plane from a kit alone is a tremendous amount of work.
I suggest building from a kit.
A more realistic design and build from scratch project is rockets.
You can have catagories like highest altitude, fastest, perhaps and egg lift. There are altimeters for even the smallest rockets that can measure altitude and acceleration. (I fly high power rockets along with my RC hobby)There is even software thet you can plug your design into and do a test flight. (Rocsim)