The City of Portsmouth Boys' School has existed in various forms since 1905. The original main campus building consisted of a red brick three floor complex surrounding an inner grass quadrangle or 'quad'. This square complex forms the oldest part of the school today, facing London road. It is currently used for the administration, history and computer departments, as well as the library. In 1944 the school became a technical college, second in the tier of the three school system (above secondary modern status and below Grammar). Under the tripartite system of the Butler Education Act, the school was expanded beyond the original main square complex.
In 1974 the school switched to the comprehensive system and the school was rebuilt in its present form that exists today. Until 1984 the school had occupied premises on two sites, the Main Campus off London Road, Hilsea (previously the Technical High School) and the Lower School in Doyle Avenue (previously Hilsea Modern School). The new building, consisting of mainly pre-fabricated materials and glass, more than doubled the size of the school. The original 'quad' building was incorporated into a new glass and concrete complex, that included a five floor tower containing the English and Science departments.
Other new buildings included new dining facilities, a new modern sports complex with two gymnasiums and a new main hall and auditorium (which contains trophies and plaques dating to the school's formation). The technology department was established a few years later and extended away from the school. At this time, the school also developed its own Combined Cadet Force as well as securing land to double the school sports field.
In the mid 1980s the technology department was extended with a new building above for the new school art department. In 1988 the school was again extended. A new music department and a new food technology department were constructed to the side of the 'main' quad building and science tower. After the education act of 1996 the school chose to become a grant maintained status school, investing financial authority in the school governors. In 1999 the school had saved enough money to build a new maths department separate from the main school complex and consisting of eight new classrooms. The old maths department, housed in temporary facilities since the 1950s was demolished.