In the District of Columbia, only police officers and members of the military (in the course of their duties only) can lawfully carry loaded firearms. Thus, security personnel who work in an armed capacity must be commissioned as District of Columbia Special Police Officers in order to carry a weapon (this law does not apply on federal property, so security personnel who work in federal buildings do not have to become DC SPO’s, although their guns may not leave their building under any circumstances).
They security at Sidwell are armed, which is why their advertisement for a security opficer requires an SPO licence.
you can be an spo and not be armed