Chris Bonnor, a former president of the Secondary Principals Council and former principal of Asquith Boys High, said Australia had established a tiered education system that was segregating students by income level and academic performance.

''We are separating our schools for the academic elite,'' he said. ''Schools which can do so are hunting out bright kids through tests, scholarships and interviews with parents and avoiding kids with learning difficulties,'' he said.

''There is also a worsening social class division with low-income children increasingly going to public schools and the richer kids going to private and selective schools.

''There is an increasing separation of kids along academic and social lines and, to some extent, along religious and cultural lines and nobody in government departments or government wants to talk about it.''

Richard Teese, a specialist in school systems at the University of Melbourne, said the expansion of selective schooling in NSW - there are now 17 fully and 28 partly selective high schools - was creating ''engines of high academic success'', but at a significant cost.

''It's a very inequitable policy because it takes away cultural and academic resources from many sites and concentrates them into a few,'' Professor Teese said. ''By operating schools like these you drain talent from many other comprehensive schools, which need what the French call pilot students - that is, model students who provide a really good example.

''The aim should be high standards everywhere. It doesn't make sense to have half a system that works and half a system that doesn't,'' he said.

Mr Bonnor, co-author of the book The Stupid Country: How Australia is Dismantling Public Education, said when two selective schools were established in the Hornsby area 15 years ago, surrounding schools were told this would provide more choice.

The schools made selective, Normanhurst Boys and Hornsby Girls, dramatically increased their share of high achievers, but the nine surrounding comprehensive schools and the low-fee private schools ''lost out''.

But the principals of those schools are in effect silenced about losing their best academic talent for fear of exacerbating the situation.

''I didn't say it when I was principal at Asquith Boys High. It has the danger of increasing the loss of the remaining high achievers from the school,'' Mr Bonnor said.

''We also now have an outbreak of pseudo-selective schools - both private and public - each setting tests to gather a disproportionate share of the able, the engaged and the anxious. This is especially taking place across northern Sydney.''

The principal of one selective high school, who did not want to be named, told Fairfax Media that selective schools had been a disaster for comprehensive schools.

''My own view is if I were to wave a wand and start again, I would not have any selective schools or independent schools or private schools or public schools. I think the model I'd like to go for is your local community school. But that's 150 years too late. We've moved on so that's no longer possible.''

The government increased the number of selective school places by 600 to 4133 this year to help stem the drift from public to private schools.

The move will also increase the ranking achieved in the HSC results by the top selective high schools. James Ruse Agricultural High School has topped the Herald's HSC performance list for 14 consecutive years.

Last year, government selective high schools took out four of the top five positions.

The first comprehensive government high schools to appear on the Herald's list were Killara High School in 54th position and Cherrybrook Technology High School in 59th.

Mr Bonnor said the Department of Education ''pretends this problem does not exist''.

''The department is avoiding the issue and no one wants to know that by offering opportunities for some kids, this is reducing opportunities for others,'' he said.