In 1957, through subsidies and other financial measures, the Sinclair Act encouraged small towns in Maine to organize into districts with a minimum high school enrollment of 300 students.
In February 1966, Cumberland and North Yarmouth merged school districts, officially forming Maine School Administrative District 51, and Greely Institute was renamed Greely High School. The school committee made plans for further additions, including a new gymnasium, swimming pool, auditorium, music room, and locker rooms. As part of the transition from Cumberland’s independent school district to MSAD 51, the committee also made plans for a 16-room elementary school with a multipurpose room, kitchen facilities, and an administrative section, with room for expansion.
In September 1966, the Board of Directors voted to name the school for Mabel I. Wilson to honor her commitment and involvement in
the local school system. The school was ready for occupancy September 1967.
