Question: What would happen if an 18 year old went on school grounds with a knife on her side after school to pick her cousin up and was caught?
Answer: Depending on what kind of knife it was, it could be classified as a 'deadly weapon' according to Arizona Law (ARS § 13-3101(A)(1)), which says that 'deadly weapon' means anything that is designed for lethal use.' If the knife fits this category, the 18 year old could be charged with 'Misconduct Involving Weapons' because it is absolutely prohibited to posses a deadly weapon on school grounds (ARS § 13-3102). 'Misconduct Involving Weapons' is a class 1 misdemeanor. If the 18 year old threatened anyone while on school grounds, she could be charged with 'Disruption of an Educational Institution,' a class 6 felony (ARS § 13-2911). If she went to the school intending to threaten someone while there but did not actually do so, it would be a class 1 misdemeanor (ARS § 13-2911). She could also possibly be charged with 'Criminal Nuisance,' which is a class 3 misdemeanor (A.R.S. § 13-2908).
Finally, school administrators could certainly ask the 18 year old to simply leave the school premises.