In the early 1950's changes occurred in the membership of the Association. St Patricks had become too small to compete effectively against the other schools and withdrew from the Association in 1951. Christian Brothers College, Perth [Terrace] and St Aldephonsus, New Norcia, were invited to join and did so in 1953. The Principals were Br M.S. Quiligan and Br .......................? The colours of these schools respectively were green and blue and blue and black. St Joseph's School, Subiaco was also invited to join at this time and did so in 1954 in the junior section of the athletics. It participated fully in Association competitions for the first time in 1956. The Principal was Br Lucian Gerber and the school colours were maroon and gold. St Louis School, Claremont was also invited to join at this time, but didn't do so as an associated member until the 1970's. It competed occasionally against member schools on a social basis during the intervening time. The school colours were grey and blue.
In the late 1950's a senior cricket competition was commenced and was won first by ......................? in ......................? At this time the Association became more formalised with regular meetings being conducted between Principals and Sportsmasters. The name of the Association was changed to Associated Catholic Colleges [ACC]. The rotating system for President and Secretary continued to operate and the two new schools were placed on the roster. Br A E Travers was Secretary a number of times during the 1950's due to his transfers between C B C schools. Br G N Edmonds was an outstanding coach during the late 1950's and early 1960's. He raised the standards of the competitions, particularly in swimming and athletics.
In the early 1960's, standards in the athletics and swimming competitions were further improved with the use of the Empire Games facilities after 1962. The athletics competition was transferred to Perry Lakes Stadium and the swimming competition was transferred to Beatty Park Aquatic Centre. In 1962, Terrace was re-located and given the new name of Trinity College. It continued under this name as a member of the Association. In 1966 the first Cross Country running carnival was held and the winner was CBC Leederville.
During the 1960's a group of junior high schools (Catholic) formed an association called the Metropolitan Catholic Colleges [MCC] to conduct interschool competitions in swimming and athletics and lightning premiership carnivals in football. Membership was a flexible arrangement, but the main participating schools were Xavier College (blue and white); De La Salle College, Midland (green and red); Keaney College, Bindoon (red and gold); St Joseph's Clontarf; St Joseph's College, Northam and Mazenod College, Lesmurdie. Other schools with some participation were St Brendan’s College, Hilton; St Norbert College, Queens Park; St Edmund's College, Collie. The Secretary-organizer of these competitions over a period of about ten years was Br P C Grant (Xavier College).