You can do SO MUCH with tofu that I think we need a bit more guidance to help out. Does it have to be a hot dish, or would a cold dish be better? Will you make this at home and bring it in, or will you have access to a stove/oven at school so you can serve something piping hot?
My mom made me Shake and Bake Tofu from "The 5-Ingredient Vegetarian Gourmet" cookbook - that's super easy and good, but it's best to serve it hot out of the oven. (I like it with their Peanut Sauce, which can be made ahead. A marinara sauce would probably be good, too.)