It makes sense at that school. It’s only a few blocks away from the San Francisco County Jail, located in San Bruno. From time to time, inmates escape, causing havoc in the area until they’re caught. Now the school’s security would be able to defend the students from escaped inmates. On a side note, the school is right across the street from the neighborhood that burned down in a gasline explosion and fire in San Bruno. The school was lucky not to burn down.
I'm not aware of escaped inmates attacking schools but, whatever, this makes sense for any school unless officials start allowing armed teachers.
It’s pretty close to the jail, you are correct.
I used to mountain bike in the area; there’s an old abandoned lookout station above the jail on the hill.