 The school was opened on 1 September 1985, when Dunlambert Boys’ Secondary School amalgamated with Graymount Girls’ Secondary School and Mountcollyer Secondary School.The new school was established on the Fortwilliam Park site of the former Dunlambert School, which was founded in 1958, and, at its peak, accommodated 1,000 pupils.Castle High School was the beneficiary of a remarkably historic site