The Seattle Academy Upper School is a member of the Metro League, consisting of eighteen schools within the Washington Interscholastic Activities Association (WIAA) District #2. League membership establishes guidelines and regulations for scheduling games and practices, equalizes competition, conducts league meetings as well as determines championships and advancement to seeded allotments in the district tournaments. The league provides Seattle Academy the opportunity for competition with schools of similar size, location, and programs. Membership requires that participating schools abide by all league rules and regulations.
The Middle School athletic teams compete in the Cross Town Middle School League and in some sports, the Catholic Youth Organization (CYO) league.
Additionally, several Seattle Academy teams participate in sport-specific leagues:
- Ultimate competes in the DiscNW League.
- Lacrosse competes in the following leagues:
- SMYLA (Seattle Metropolitan Youth Lacrosse Association) for Middle School Boys
- WSLA (Washington Schoolgirls Lacrosse Association) for Middle School and Upper School Girls
- WHSBLA (Washington High School Boys Lacrosse Association) for Upper School Boys