[2] The founders were prominent New England educators, businessmen, and civic leaders, including Ernest Martin Hopkins (president of Dartmouth College), William R. Brewster (headmaster of Kimball Union Academy), and Ralph Flanders (a U.S. senator from Vermont).

The founders believed the location to be ideal for a boys' school: the land and Haffenreffer mansion, which initially housed classrooms and a dormitory and is now called Clark-Morgan Hall, are situated on a peninsula in Canaan Street Lake with views of Mount Cardigan and the White Mountains to the east and the Green Mountains to the west.

[3] Cardigan Mountain School runs its Summer Session usually beginning in June and ending in August.

Summer Session, unlike the academic year program, is coeducational and serves younger students (grades three through nine) for three- and six-week experiences that include academic enrichment classes in the morning, and summer-camp style activities for the rest of the day.

participants experience week-long trips that may include hiking, camping, canoeing, kayaking, and outdoor education programming.