there is also a legal term "in plain sight"
the plain-sight rule says
"Plain sight rule is a principle of criminal law that permits a police officer to seize without warrant and use as evidence any item seen in plain view from a lawful position or during a legal search when the officer has probable cause to believe that the item is evidence of a crime.
The "plain sight" rule recognizes that no citizen has a reasonable expectation of privacy with respect to unconcealed items within a vehicle in police custody.[State v. Gowans, 500 P.2d 641 (Ariz. Ct. App. 1972)]"
if a police officer sees some illegal activity or illegal item in plain sight - say through a window from the street or in a car - they can act upon what they see
so if the school staff member is acting as the legal agent based on some information of suspected misbehavior
and the standard procedure is examine the computer, including the browser history for inappropriate behavior, and when clicking on the netflix history record it opens netflix (saved password) and shows an inappropriate movie has just been or is being viewed - the plain sight rule might apply
if the school staff member explores further into the netflix account - that might be going beyond plain sight - or it could be legal under just cause to investigate behavior on school equipment
i'm not a lawyer - i just play one on my laptop...