I've heard criticism against the movie both for being too sad and too optimistic in its ending (from different sources in a discussion at a university event I attended). Although I didn't expect the ending to happen where it did, I think it's left completely open as to what's going to happen next and is neither sad nor optimistic; I think you're set up to be able to write several more diametrically-opposite scenes after the ending depending on how Michael's girlfriend reacts, along with the other kids and their parents and school.