In 1927 a new wing was opened, containing four new classrooms, an art room, two storerooms and a cloakroom.

In 1959 the gym was added as well as what was for the next 25 years to be known as the "new block", the building containing laboratories and classrooms.

Until 1974 it was administered by the City of York Education Committee, then North Yorkshire County Council until 1985.

In 1985, due to the acquisition of the site by All Saints RC School, the building was repurposed into the catholic school's upper site, in order to allow the restructuring of catholic secondary education in the Vale of York.

After local government reform in 1996 authority for the school was transferred to City of York Council.

[2] However Millthorpe School continues to coordinate with City of York Council for admissions.