The oldest part of Thorne Grammar School is of typical design for 1930s schools consisting of long classroom ranges joined at right angles by large assembly halls with central 'quadrangle' areas to allow light into the building. The school appears to have been much enlarged by the construction of modern buildings to the north west of the core and the addition of a junior school at the other end of extensive playing fields in the late 20th century. Some of the plot boundaries give fragmentary legibility of the surveyed enclosure of North Field in 1825 (see Haywood).