Four years after the conference's formation, membership expanded to ten with the addition of Darien, Norris Foundation in Mukwonago, Union Grove and Walworth.
In 1937, Clinton, Darien, Genoa City and Williams Bay would leave the Southeastern to form the Southern Regional Conference along with Capron (now North Boone) High School in Illinois.
[6] Membership would continue in this configuration for sixteen years before East Troy, Mukwonago and Wilmot left to join the new Southern Lakes Conference in 1953.
[10] Slinger left to join the new Scenic Moraine Conference in 1958,[11] and they were replaced by three returning members and one newcomer.
Four of its members (Salem Central, St. Mary's, Union Grove and Waterford) formed the new Southeastern Badger Conference,[16] while the other four (Clinton, Norris Foundation, Palmyra and Williams Bay) joined with Northwestern Military and Naval Academy in Lake Geneva and Wisconsin School for the Deaf in Delavan to form the Indian Trails Conference.