Until 1963 Southwell was a private school, owned by the family of the late Mr H G Sergel: Rev Canon P C S Sergel, Mrs N R S Johnstone, Mrs J S Cumming and Mrs A I Sandford.

In that year the family gifted the School to become a non-profit making Educational Institution to be administered by a Trust Board under the terms of a formulated Trust Deed. The Trust Board is a self-appointed body comprising no more than twelve members, including the President of the Old Boys’ and Girls’ Association, and the President of the Southwell School Association during their terms of office. The Board elects a Chairman for a three-year term and has three main sub-committees: Audit and Compliance, Strategic Planning, and Governance. The Trust Board meets twice every term.