Sion Hill was founded by the Dominican Sisters in 1836. It was in a suburban villa, which they called Sion Hill because of rare shrubs brought by its owners from the Holy Land. In the beginning, the school catered for 40 day pupils, 8 boarders and 10 nuns. By 1950, this had increased to 120 day pupils and 130 boarders. The boarding school closed in the late 1960s and the school now caters for 350 day pupils.
From the beginning, the curriculum was comprehensive. Records from Prize-Giving in 1876 show that the following subjects were taught:
Music (instrumental & choral), History, Christian Doctrine, English, French, Geography, Italian, German, Orthography, Art, Sewing, Arithmetic, Politeness and Flower Modelling.
In the immediate aftermath of the Intermediate Act 1878 and the Royal University Charter 1880, students were prepared for public examinations.
Records from the early part of the 20th century show that subjects added included Irish, Classics, Bookkeeping, Shorthand, Typing, Scientific Dressmaking, Domestic Economy, Physical and Natural Sciences, Swedish Drill and Games.