When Ahmed Mohamed was arrested for his clock, prejudice may have played a role, but "zero tolerance" played a role too.

If someone brings a real bomb into a school, that is a real threat and calls for a real response. But there was never any serious reason to believe Ahmed's clock was a bomb, and the thugs must have seen quickly that it lacked the crucial ingredient of any bomb: explosive. So why arrest him then? "Zero tolerance", the idea that being mistaken for a threat makes you guilty.