The police detained him until they could investigate the device and question him about his intentions, then released him. Sounds like a rough afternoon, but hardly a ruined life. He's been released and he's exonerated.
Hopefully some will learn that reasonable and probable cause needs to have some basis in certain priori, and that opportunity cost and the boy who cries wolf are really and very harmful issue.
I put the security of a school full of other kids above the 'opportunity cost' of being questioned by police. I'm guessing many other people would as well - especially the parents of the other kids at the school.
understand that P(massacre | kids = 14 years old in the US) is some number that probably is smaller than IEEE floating point error, then everyone will be better off for that.
Past performance is no guarantee of future results. Just because it doesn't happen in the US often, doesn't mean it won't. 14 years old are involved in violence all over the world, especially in bombing incidents.