Alternate and much more depressing prediction: "Normal" kids won't want to use an app for bullied (i.e. "weird") kids in general. Some bullied / non-conformist / nerdy / queer / alt / etc kids will try to use it and probably enjoy it. Then some bully will discover that they can post an open lunch table to find out who's using the app and then humiliate them, perpetuating the cycle.

edit: ... but I still love the idea.