i would have to disagree with the comments saying that there are more opportunities at private schools...
I would rather like to perhaps rephrase that there "might" be more motivation to do well at private schools.
With parents forking out thousands of dollars to send their kids to school, and the actual discipline policy at private schools, you would probably have more motivation to do well at such schools compared to a comprehensive state high school.
But assuming the motivation is there, the marks would be no different between a private and a non-private school.
When you think about it, what does a private school provide that a public school doesn't in terms of doing the HSC. The teachers are the same in qualifications, the resources are the same, and although class sizes "may" be smaller in private schools, i dont see this is such a huge issue (considering that 24 is max at govt schools and i dont see any real problem with it).
Thats what im saying. By the way, i am not bagging out private schools out, or saying that you shouldn't waste your time going to one, but all im saying is that in terms of academic success there is no advantage.