Places
Possessing Firearms / Dangerous Weapons on School Facilities.
Yes, Washington does prohibit firearms on school grounds. But the law has many exceptions to it. The applicable statute, RCW 9.41.280 reads https://app.leg.wa.gov/RCW/default.aspx?cite=9.41.280
Licensed Day Care (child care) Facilities.
https://app.leg.wa.gov/RCW/default.aspx?cite=9.41.282
There are prohibitions against possessing firearms at voting facilities.
https://app.leg.wa.gov/RCW/default.aspx?cite=9.41.284
There are several other places where you cannot carry a firearm under any circumstances.
Courthouses, jail facilities, any place designated by Washington law as age 21 and older are just a few of Washington's restrictions. You can see all of them here. https://app.leg.wa.gov/RCW/default.aspx?cite=9.41.300
Special rules regarding the State Capitol Grounds in Olympia.
https://app.leg.wa.gov/RCW/default.aspx?cite=9.41.305
Outdoor Concert Venues.
Washington law prohibits the possession of firearms, by anyone except law enforcement, at all outdoor concert venues. https://app.leg.wa.gov/RCW/default.aspx?cite=70.108.150