The main block of Christchurch Boys' High School was designed by J. S. and M. J. Guthrie and completed in 1926. The Guthrie brothers designed many residences in Christchurch, as well as the well-known Edmonds Factory building (now demolished). The school itself had begun in 1881 in a two-storey stone building on the former Canterbury College site, which is now the Christchurch Arts Centre. As the size of the school grew, the original building became too cramped and land in Riccarton was purchased for a new school.

The new school building had a central administration section flanked on both sides by a wing of classrooms. It incorporated contemporary principles for school buildings, yet also made architectural references to the earlier building the school had occupied when it was established. Ideas about the benefits of open-air schooling were prevalent at the time and some of these were incorporated into this building - including large windows facing north, and open corridors on the south side. (These corridors were enclosed at a later stage.) On the other hand reference was made to the school's history by the incorporation of two columns taken from the original building within the entrance porch of the new.

The Main Block continues to be used as part of Christchurch Boys' High School, although under threat from demolition for many years as it was thought to be an earthquake risk. The building is significant as part of Christchurch's architectural heritage and as part of the school's history.