One bright child from a poor background might still thrive in any government school but when there are clusters of impoverished students, they tend to drag each other down.Basic issues such as regular attendance have become huge endemic problems in Disadvantaged Schools. See my article Optimism and Reality in Disadvantaged Schools.
Ever since the Disadvantaged Schools Program (created by Whitlam, axed by Howard in 1996) was removed this had been the growing trend. Howard's intention is to further strengthen the social class distinction, which has always been there, through the Private / Public school division.
The Rann governments response? Put up the School leaving age without providing extra resources for schools.