In 1940 the school was evacuated from the south coast of England, to Wales, initially to the Oakeley Arms Hotel, Tan-y-bwlch, Merioneth, and later to a former workhouse in Cors-y-Gedol Hall, near Barmouth, until the end of the war.

The school moved to its present site at Pease Pottage after World War II in 1946.

The school is housed in a Grade II-listed[4] Victorian mansion known as Buchan Hill that was built in 1882–3 by Philip Felix Renaud Saillard.

[5][6] The building is a large Elizabethan-style house, designed by the architects Ernest George and Harold Peto.

In 2023, Cottesmore appointed the first AI headteacher, which they named Abigail Bailey, to assist the human headmaster.