[1] Founded in 1905 to "create equitable playing conditions"[1] between member teams, the WIAA plans and supervises interscholastic sports and activities approved and delegated by the various school district boards of directors.

In addition, the WIAA recognizes achievement and excellence of member teams and individuals participating in sports and activities.

[1] Additional funds are secured through corporate sponsorships, memberships fees, and small percentages of the sales of merchandise related to the organization and its member schools.

As a private organization, the WIAA does not receive any funding via tax dollars and is not financially supported by the State of Washington.

Classification tiers are based on student body enrollment in grades 9–11 and used by the WIAA to maintain fair and equal competition between its member high schools.

The enrollment ranges are evaluated by the WIAA Executive Board every four years and finalized for a four-year period.

If a school chooses to opt up, it must notify the WIAA office on or before the second Friday in January of the first year of the four-year classification cycle.

Its membership consists of high schools in Snohomish, Island and north King counties, in and near Everett.

Its membership consists of high schools in western Whatcom, Skagit and counties, in and near Bellingham and Mount Vernon.

Its membership consists of small public and private high schools in San Juan, Snohomish, Skagit and Whatcom counties.

[24][25] For the 2020–21 school year, Cheney moved up to 3A; with only four teams left in the GNL, that league was folded and absorbed into a new GSL 2A division.