The school was established in 1926 by Jessie Elliot-Pyle in Brownlow Road with three pupils, and was named after Dunnottar Castle in Scotland.

She chose for the school's crest a pelican mother nurturing her young.

In 1933, the school moved to the High Trees Estate in a mansion called "High Trees"[2] which had been built by Walter Blanford Waterlow, fourth mayor of Reigate, in 1867.

[7] Other recent developments include a £240 million Sixth Form Centre, opened in April 2019, and the £786 million construction of The Castle Theatre and Performing Arts Centre, completed in January 2021.

[8] The school premises is a grade II listed building,[4] and the grounds are adjacent to Redhill Common.