Here's an interesting ABC Life Matters podcast about a new report entitled Who's afraid of a public school? commissioned by independent think tank Per Capita. It calls on middle and high income parents to act in the greater good and opt for the local government school and resist the temptation to choose independent schools.
No one expects parents to "sacrifice their children on the alter of ideology", says co-author Verity Firth, but it seems that when you look at the data on an individual student basis, there's no sacrifice involved in choosing public education, only money to be saved. The chief determinate in academic performance, it seems, is not the school a student attends but the socio-economic status of their parents.
N.B. UK readers, what you call "public schools", Australians call "private schools", and what you call "state schools", Australians call "public schools".