Complex sentence: It is the site of Claremont High School, currently being redeveloped and expanded to form the new Calderglen High School which will accommodate the pupils of both Claremont and Hunter High Schools.
Split into simpler sentences: It is the current site of Claremont High School, currently being redeveloped and expanded to form the new Calderglen High School. This new school is planned to accommodate the pupils of both the existing Claremont and Hunter High Schools.