The school thought it could possibly be a bomb.
Why was the boy from Texas arrested for bringing a clock to school?
Sheer stupidity, religious persecution, and "zero tolerance" rules.
He wasn't. The boy was arrested because somebody from the school was working with the media and they thought it would be a great headline, and get lots of attention.
He definitely wasn't arrested for bringing a bomb though. They didn't even treat it like a bomb.
