What are we teaching?

I hadn't been following this story until today, but I have to stop and ask "what are we teaching our children when we give them a punishment with potentially long lasting punitive impacts for doing something that has the potential to cause harm?"

That feels too much like a scene from Minority Report, in which the police have a way of predicting future crimes with very high but not perfect accuracy.  The preemptively arrest people for crimes that those people haven't even contemplated committing, yet.

In the case of kids bringing weapons to school, what does it teach out kids that if they make a mistake, they'll be kicked out of school.  No second chances.  No chance for rehabilitation.  No opportunity to teach them about appropriate behavior and safety.  It seems to me that our schools should be both safe and a place for teaching, not just by making an example of others but also by experiencing situations.

I recognize that there are rules to prevent dangerous situations.  I'm not questioning the rules in this argument as much as I'm questioning the punishment.  (Making rules more practical is for a separate argument!)