The school's grounds cover 36 acres (15 ha) situated on the edge of Ascot (actually in Bracknell Forest), providing access from London, the major airports, the M3 and M4 motorways.

[citation needed] The school was run by the sisters of the Community of St Mary the Virgin and was based in the Queen Anne house on Newbury Street.

Sister Annie Louisa was responsible for the chief structural improvements at St Mary's including a science wing and the conversion of an old barn into a gymnasium.

By the time Sister Annie Louisa left in 1919, St Mary's was recognised as a "public school with an unusually high standard of scholarship".

Girls in Wyatt House live in separate accommodation similar to that of a hall of residence to prepare them for university life.