Schools are one of the places where weapons of any type are prohibited. The only people allowed to have a weapon in schools, usually, are police and military personnel. Doesn’t mean they don’t enter the school but you can get in trouble if your caught.
In my school the Military exception included students who were part of the JROTC drill or rifle teams and currently engaged in an activity associated with that team while in uniform. Drill team could carry their M1s to, during and from drill practice for example.
JROTC stands for Junior Reserve Officer Training Corps. Basically it’s a down sized military academy operated within a normal school, sort of. Mostly you learn survival and field medical skills.