There are only two scenarios here that are tenable. Either he built a real bomb and brought it to school or he didn't build a real bomb.
If he didn't build a real bomb then the question becomes whether or not he attempted to scare people with a hoax bomb.
Unquestionably he didn't build a real bomb. Moreover, he didn't attempt to scare anyone with a fake bomb either. He brought a clock to school. He insisted to everyone that it was a clock. And he tried to avoid showing it to people.
That is not a hoax bomb in any sense of the word. If you don't have a hoax bomb and you don't have a real bomb then what do you have? Panic, and bigotry. Nothing more.
Zero-tolerance policies are their own can of worms, but neither such policies nor any possible explanation of their enforcement explains the characterizations made after the fact by both school and law enforcement officials regarding the supposed "hoax bomb".
http://pol.tasb.org/Policy/Download/367?filename=FOD(LEGAL)....
These are the relevant documents. They are short enough to read them in less than 5 minutes. Can you tell me what the legally-mandated punishment is for bringing a non-weapon that resembles a weapon onto school grounds is?
It's easy to bikeshed about "characterizations", but there are legally no other ways the school district could have reacted on the day they were making decisions.
Can you explain the relevance since -- except in the sense that every digital clock in existence resembles a fictional weapon through the Hollywood tendency to depict bombs as digital clock displays -- the actual device in question does not in any meaningful sense resemble a weapon.
Further, you answer your own question.
Remember that chicken fingers qualify as weapons under these policies.