Currently, it is against the law for anyone to pack heat on school grounds in my state, except police officers. It is so extreme that a child with a GI Joe doll sized toy pistol(about the size of a quarter)was suspended from school for bringing that toy to class.
Now I thought the same thing about my state due to the signs on the building but, after speaking with a police officer who happened to be quite knowledgable in the area he stated that A) there is no case law on the subject B) the law says only those that are "licensed" to carry a weapon may do so on school property and C) if he were to come across someone who is legally licensed to CCW on school property he would not sound any alarms.