St. Paul's was also a member of the Independent School League (ISL) until 2017. The school announced the decision to withdraw from the ISL in 2016 due to league bylaws surrounding scholarships. Since the 2017–18 academic year, the school competes in the Six Schools League (SSL) with Choate, Deerfield, Northfield Mount Hermon, Andover, and Exeter. Additionally, the school competes in the Lakes Region League with Proctor Academy, New Hampton School, Kimball Union Academy, Tilton School, Holderness School, Vermont Academy, The White Mountain School, and Brewster Academy.