To back up what Bear (and quentusrex) are saying, here are the relevant portions of RCW 9.41.280 :
Among other things, this section is Yet Another Example of how badly-drafted so many of our laws are--(5) says that (3)(f) contains an exception to the ban on bringing firearms into school buildings, but (3)(f) actually says the firearm has to be left in the car.
(1) It is unlawful for a person to carry onto, or to possess on, public or private elementary or secondary school premises, school-provided transportation, or areas of facilities while being used exclusively by public or private schools:
(a) Any firearm...
(3) Subsection (1) of this section does not apply
(e) Any person in possession of a pistol who has been issued a license under RCW 9.41.070
, or is exempt from the licensing requirement by RCW 9.41.060
, while picking up or dropping off a student;
(f) Any nonstudent at least eighteen years of age legally in possession of a firearm or dangerous weapon that is secured within an attended vehicle
or concealed from view within a locked unattended vehicle
while conducting legitimate business at the school;
(g) Any nonstudent at least eighteen years of age who is in lawful possession of an unloaded firearm, secured in a vehicle while conducting legitimate business at the school; or
(5) Except as provided in subsection (3)(b), (c), (f), and (h) of this section, firearms are not permitted in a public or private school building.
But also note that (5)'s list of exceptions does not include (3)(e) (regarding dropping off or picking up a student), so I'd have to conclude that the schools folks were right about the inside-the-building part, and the police wrong, in 911's incident.