In November 1935 the foundation stone for a new assembly hall, dining room and kitchen was laid by Lady Lansdowne. Built of reclaimed stone from the old Calne workhouse which the school had bought in 1934, when completed the building stood proudly above the lower grounds of the school.
One of St Mary's early school houses had been given the name St Faith. The tradition continued with two further buildings named St Prisca and St Bridget. The Headmistress, Marcia Matthews, wanted these three saints associated with the school to be represented in relief work on the face of the new building. However, the architecture of the assembly hall called for four plaques and as the hall would be extensively used for music, St Cecilia, the Patron Saint of Musicians, was included.
When the early school on The Green in Calne needed more accommodation, an adjoining house was bought which became known as St Faith's. The name was reused at St Mary’s new school site when a boarding house on North Street was rented in 1928. St Faith's was bought by the school in 1948 but later sold.
St Prisca’s, a boarding house now within the school grounds, was the first property bought after the school moved to it new site in 1907 and needed to extend beyond the grounds of School House. A tall building, it has been added to several times since its acquisition in 1919. At first it provided dormitory space and a Domestic Science kitchen, and was the location of the junior department of St Mary’s.
St Bridget's was the name given to one of St Mary's boarding houses in the centre of Calne. Previously known as Congresbury House, it had been conveyed to the school in 1929 after having been rented to it for some years by one of the alumna, Agnes Buckeridge. In 1967, when there was adequate boarding on site, St Bridget’s was sold.
In 1943 a house on the edge of the school grounds was acquired as a boarding house and took the name St Cecilia's. Previously called Northfield House, it had a fine garden which is now incorporated into the school grounds. The house has been described as 'a good example of an 18th century semi-detached house' and in the 19th century had been used by the local doctor as an asylum. Part of the garden was used to grow opium poppies 'to sooth his patients'. In 1956, St Mary’s bought the other half of the building to enlarge the boarding house.