In the novel, reference is clearly made to his own alma mater, St Aloysius' College, as the description of the fictional school, St Ignatius',  is clearly a description of the buildings and environs of the school Cronin attended.
In the novel, it is made clear that Cronin's own educational background at St Aloysius' College is the basis for the depiction of the fictional school, St Ignatius', with its description being a direct representation of the actual school Cronin attended.