Christ's College began in April 1851 as the Collegiate Grammar School, run from two rooms at the immigration barracks at Lyttelton. The Canterbury Association, the group formed in England to colonise Canterbury, had planned for such a school before its ships left England, stating that it was to be based on 'the great Grammar Schools of England'. It is now the oldest and one of the most prestigious private boys' schools in New Zealand.

In 1852 Collegiate Grammar moved to Christchurch and by 1857 was established on its current grounds adjacent to Hagley Park. The buildings of the school were laid out around a quadrangle following the English tradition, and were initially built in timber. Between 1855 and 1862 the roll increased by 50 pupils and new schoolrooms were required. James Edward FitzGerald (1818 - 1896) proffered architectural plans for the school building he had drawn up in Britain in 1850 as part of the Canterbury Association's preparations for coming to New Zealand. FitzGerald is more commonly remembered as the first Superintendent of Canterbury and as a runholder, journalist, and politician. He took a strong interest in the development of the architecture of Christchurch, but Big School appears to be the only building he designed.

FitzGerald's building was simple and rectangular in plan, with a large and sharply pitched roof, intended to cope with the frequent and heavy snowfalls expected in the south. It was built in stone, with a timber ceiling, slate roof and leaded windows. (The ornamental bands on the roof in different coloured slates may have been added in 1896.) FitzGerald later wrote of the building: 'It was never part of any large plan. The only idea was to impress on the youngsters of that day that massive strength, stability and simplicity of character were the lessons it read to them', all virtues traditionally taught by the public schools of England.

The whole school was taught in the building, with classes partitioned off by curtains. The interior was gloomy, as the windows were whitewashed over. The interior was panelled in 1900 and in 1910 panelling was continued around the west side as a South African (Boer) War memorial.

As other classrooms were built throughout the 1870s and 1880s, Big School was used less for teaching. However it continued to be used for assemblies, concerts and speeches as well as evening preparation. It was used for assembling the boys before chapel until the late 1930s when the still-growing roll made the building too small. During the Second World War it was used as a gymnasium, as the school's regular gymnasium had been commandeered by the Army. Later it was used for badminton and drama rehearsals. While the College Chapel was being reconstructed in 1955 - 1957, Big School served as a builders' storeroom. In 1958 it was modified for use as the College library, as the Hare Memorial Library had by then become too small. In 1970 further modifications included a mezzanine floor, extra shelves, a librarian's room and a long dormer window.

In 1989 the building was substantially extended to the west by the addition of five gabled wings, which run at right angles to the original building. Sir Miles Warren was the architect. The interior panelling was reused and copied in the new section. The view of the building from the quadrangle remained the same.

Big School may be the oldest educational building in New Zealand still in use for educational purposes. It is significant as part of the history of the Canterbury Association, being designed by the Association's emigration agent, FitzGerald, prior to the colonists' departure for New Zealand. It illustrates the planning that was put into the establishment of Canterbury, albeit based upon a bleak notion of the province's climate. It shows too, the determination of the Association to replicate England in a new country. The building is an important part of the College's complex of buildings, which forms a significant part of the Gothic Revival townscape of Rolleston Avenue. The 1989 extensions complement the original building and were award-winning in their own right.