Well, I'm gonna be the devil's advocate here. First of all, it appears that the girl was able to walk to the nurse's office, so her attack, while bad, did not appear to be life-threatening. Second, they could easily have phoned 911 from the nurse's office and gotten emergency medical permission from a doctor if it was necessary. Third, the fact that the parents had given permission is irrelevant, unless one of the parents is a doctor; if it was that much of a concern to them, they should have talked it over with a physician and given each of the kids permission in writing, and even provided the school with a copy. (I know, hindsight is 20-20).
Fourth, it appears to have been the police, not the school, which arrested the youth. so blaming the school authorities may have been unfair. (Granted, the laws in the US nowadays are getting ridiculous - but giving someone prescription medications when you are not qualified to do so, and without medical approval, is illegal and for good reason.)
Fifth, as was pointed out, the charges were dropped within two days. (It appears the boy was charged, given a date to appear in court, and released, rather than being hauled off in handcuffs.)
It may seem unfair, but the school has only the teen's word for it that the prescriptions are identical, and therefore, IMO, they were duty bound to report the incident to the authorities.
If the parents had discussed this with their doctor and provided the school with written permission, rather than just telling the kids it was okay to swap medicines, this incident might well have been avoided.
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"The mind is not a vessel to be filled but a fire to be kindled."
-Plutarch