I spent my childhood in a large urban public school system. I went to the best Elementary, Junior High, and High Schools in the city. Pretty much every other school had as much or more security than those I went to. All three schools had CCTV cameras in the hallways, public spaces, my high school also had them in many classrooms. I was shocked when I arrived to college that there are no cameras anywhere indoors.
Elementary School (K-6): 500+ person school. Maybe a couple private security guards without weapons.
Junior High (7-8): attendance fluctuated as the school was under renovation, it's over 1,000 now, largest in the city. There were frequently fights between students. The school had 2-3 assigned police officers. I believe they had guns. In addition there were at least a dozen private security officers. The school was run like a prison (I've heard since that this has changed). Metal detectors at the front doors and all other doors were locked (it was a big deal to get caught sneaking through other entrances). Security guards had bullhorns and barked orders at you from across the hall. Absolutely no freedom to move around the building without explicit permission from staff. The school had a daily announcement five minutes before the end of the day that "Students are not allowed to stop at establishments on their way home. Students must go directly home before going to establishments." because there was a tendency for students to start trouble at local businesses.
High School (9-12): 400 person school, smallest in the city. Much more laid back, but largely because it was a magnet school: students had to take an entrance exam, get letters of recommendations, pass interviews in order to be admitted. Behavioral problems could get you expelled and sent to a neighborhood public school instead. Because most students didn't want that, there were few behavioral problems and we had more freedoms (no metal detectors, you could leave school for lunch or during other gaps in the day). There were just 2-3 security officers without weapons. Police officers would come occasionally but none were stationed in the school.