Dating from 1892 and made of red sandstone, it is now a Category B listed building.
The building ceased to be a school in October 2010, and was divided into 24 flats around seven years later, owned by Caledonia Housing Association.
Health and safety rules meant the building's atrium was sealed off, to be made accessible only on special occasions.
The project also involved a new block, of 21 flats, constructed in the school's former playground.
Also, six additional properties were built in an annex building that formerly housed the school's gymnasium, cafeteria and after-school club.