Depends what we mean by grade school. For young kids (and honestly most adults) I don't think you need much more than this: "A wing, or anything that sends air moving past it down toward the ground will cause some lift (a push toward the sky), but also some drag (a push on your front toward your back). How much of each depends on the shape of the wing and how it's moving through the air. Really good wings cause a lot of lift without a lot of drag, which is good for not using a lot of fuel to get where you're going or for going really fast."