[2] The ISL hosts some of the nation's oldest high school athletic rivalries, including Milton-Nobles and Groton-St. Mark's, both of which date back to 1886.

[citation needed] In the 1960s and 1970s, Middlesex, Groton, St. Sebastian's, Roxbury Latin, St. Paul's, Lawrence, Rivers, and St. George's joined the league.

[11] The ISL also forbids member schools from fielding postgraduate students on their sports teams.

[5] Accordingly, future NBA player Duncan Robinson was required to transfer from Governor's to Phillips Exeter for his postgraduate year.

[15] With the exception of Tabor and the now-departed St. Paul's, ISL schools do not compete in boys' and girls' eights, where teams like Kent, Andover, and Exeter participate.