Williams chose the school's motto of "Abeunt Studia in Mores", which he had taken from Ovid's "Heroides", in which it is proclaimed by the poet Sappho in her love letter to Phaon. Williams also chose purple as the school's colour, supposedly because it was associated with war wounds and liturgical mourning, something that he and his wife considered appropriate following the death toll of the First World War. It was agreed that the school would initially take in 62 boys, of whom 52 would be fee-paying, 8 of whom would have free-place scholarships and 2 of which would be "junior exhibitioners". Fee-paying residents of either Kent or London counties were charged £4 a term, while "outsiders" were instead charged £10. Half of the first intake of students lived in Sidcup itself, while the others mostly came from neighbouring districts such as Petts Wood, Chislehurst, Orpington, Foots Cray and New Eltham. The school opened on Thursday 17 September 1931, with a dedication ceremony taking place on Friday 25 September.