Thanks for the quick reply.
Assuming that your 17 year old told you everything that transpired I don't see how the state could sustain this charge and I would expect it to be dismissed.
Here is the statute under which he has been charged. (see link)
Although he technically did threaten to commit an offense, unless this whole thing was far more dramatic than your son let on, I don't see much coming from this other than a lecture from a judge.
However, because it is a criminal offense, and because teenagers don't always put the most accurate spin on the troubles they get into, you'd be wise to have him come in with a lawyer. Criminal cases can have lifetime consequences.
Worst case scenario would likely be some kind of a diversion program where he'd be supervised, have to do community service, pay fines, and accept accountability for his behavor and stay out of trouble during the supervisory period, after which everthing would be dismissed. But depending upon the facts and circumstances this may have to be negotiated. So again, a lawyer is a good idea.
Given he's got his whole life ahead of him, it's better to be overcautious and protect his rights and future than to send him off to face the judge alone.