The Gables, in Poplar Rd, was owned by the Lysaght family. During WWI it was used as a military hospital. After the war the family sold the property and St Margaret’s girls’ school moved in. The school had previously occupied premises in Julia Terrace next door to Brean Down House School, where it had been founded in 1910 by Mary and May Cooper. The school remained at Poplar Rd until its closure in the mid 1950’s. (The Book of Burnham, Winston and Robert Thomas p. 83).
It appears that at some point St Margaret’s amalgamated with Oakover School. Advert below from 1942: