In 1975, construction of the audio-visual room gets under way. As intended, the room becomes useful as a venue for showing films, using the school projector, and later for showing videos. It is also used by girls in the Drama department as Drama is now an official matric subject – St Mary’s is the only school to offer it.

In 1977, the Trevor Williams Block consisting of four classrooms and a biology laboratory are built. The block is named for a former chairman of the Board. At the same time, the chapel garden is redesigned.

The Junior School is upgraded when a classroom is converted into the staffroom, the staffroom into the headmistress’ office, and the headmistress’ office into a sick bay.