Prediction: All kids start using this app to formalise their social circles the end result being that the outcasts remain outcasts but now they know exactly how rejected they are by the rest of the student body.
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.
A lot of these kids aren't trying to be in the 'in crowd' so much as have any friends at all. Many of them would be most happy to exist in a circle of 'outcasts'.
One of us has a major misunderstanding of how this app works.
Outcast kids are usually keenly aware of just how alone they are among their peers.