To the OP: What grade are you in? And what is the actual situation? Is this going to be for a grade, or is it an enriching project as part of an after school club?
I ask because I'm a middle school engineering teacher. I design problem solving and design projects all year long for kids and teach them the fundamentals so they can be successful. I would never tell a group of high school students to try and design an airplane when they've never flown one. Aeronautics is a complicated science with a lot of variables working at the same time. Even if everyone in your group already knew model building techniques, your chances of producing a successful scratch design would be virtually zero due to all of the interrelated issues to deal with.
If the point is for the group to work together and get something in the air, take the advice above and build one of the classic trainers like the Kadet Sr. and then get a qualified flight instructor at a proper flying facility to train you.