Very shortly after moving premises, the school was overflowing its Andringa Street building (where it had moved under the formidable Dr Marais), and rector WH Hofmeyr had to organise for the building of another storey on to the main building.
However, it was not long before this new building, at first considered so large and well-equipped, also became too small. It was decided to erect an entirely new building for the school. The new school, in Victoria Street, was duly completed at the beginning of 1907, but some administrative hiccups prevented the boys from moving in for another year. However, once they were in, they stayed for 30 years in the splendid 'Netherlands Renaissance'-style building, surrounded by leafy oak trees.
When in 1909 Hofmeyr left to take up another post in Pretoria, an Old Boy and ex-teacher of the school, Paul J Roos, was invited to become the sixth rector. This physical and mental champion was to lead the school for 30 years. Under Roos, the school rapidly acquired a South African flavour.
The decade of the 1920s saw Afrikaans officially replace Dutch in the syllabus; the design of the school banner, a modified school badge (to less resemble that of the Stellenbosch University) and a new sports colours blazer; the formation of an Old Boys' Union; and — the crowning glory of an exceptional decade — six Old Boys winning their Springbok rugby blazers against the All Blacks. In 1935 Roos celebrated his silver jubilee as rector, and the following year the school had its 70th anniversary.
Four years later the head declared that, with 540 boys on the roll and even the hall and staffroom having been converted into classrooms, the school had developed far beyond its original objectives and urgently needed more space.
Roos did not stay to see his request fulfilled, however: with tributes of respect coming in from far and wide, the school's most esteemed teacher and rector bade his alma mater farewell in 1940, and so turned the page on a most stirring chapter in its history. In the same year the school board renamed the institution Paul Roos Gymnasium.