A Fairfax Media analysis of this year's fees for some of Sydney's top single-sex and co-ed private schools shows Cranbrook broke through the $35,000 mark, charging day boys up to $35,805 to attend the eastern suburbs institution.

Nearby Bellevue Hill's Scots College and SCEGGS Darlinghurst are two of the most expensive schools in the state, charging parents more than $34,900.

The rate of growth in fees at some schools has been up to twice the rate of inflation since 2014, with charges at SHORE, Hills Grammar and Roseville rising by more than 18 per cent.

Parents at St Catherine's and Newington College are paying some of the highest fees when boarding costs are included, with both schools charging more than $60,000 for students to stay on campus. Cranbrook will charge parents $67,028 for board and tuition this year.

The new data comes as debate continues to swirl on the level of public funding in private schools.

Students attending high-income schools attract one-quarter of the amount of government funding compared with if they attended a government school, according to the Association of Independent Schools.

"The comparatively low levels of per student funding for students in independent schools is a major saving to the taxpayer," said the association's chief executive, Dr Geoff Newcombe.

"Significant numbers of parents clearly feel they are getting value for money as enrolments in independent schools continue to rise, with waiting lists at many schools full and some even closing them off altogether."

Schools such as Saint Ignatius' College, Riverview, will charge parents up to $26,940 in fees next year, despite taxpayers over-funding the school by more than 200 per cent, according to a Fairfax Media analysis of Department of Education data.

The analysis compared the recommended level of funding under the needs-based Gonski system with current levels of funding.

The school has plans to construct a multimillion-dollar "retail and hospitality hub".

Newington, which educates nearly 2000 students in Stanmore, has some of the highest levels of public funding for a top-tier private school in the state. It gained more than $9 million in taxpayer funding in 2014, the last year public funding records are available, while charging more than $28,000 per student.

The inner west's Trinity Grammar, which charged students $31,670 in 2016, is pushing ahead with construction on its "Olympic pool with underwater cameras and timers" after receiving up to $31 million in public funding from 2012-2014.

Fees at north shore schools Loreto Kirribilli and Monte Sant' Angelo Mercy College have also hit the the $20,000 mark, despite being over-funded by up to $5 million in taxpayer subsidies, according to the Fairfax Media analysis.

St Catherine's has increased its fees by more than 21 per cent over the four-year period.

The Waverley school won a battle with council and local residents last year to continue building a $63 million auditorium complete with an orchestra pit, a water polo pool and a fly tower for state-of-the-art theatre productions. According to MySchool data, it received more than $5 million in public funding in 2014.

Parramatta's King's School has spent more than $4 million on capital upgrades between 2009 and 2014, including improvements to dozens of playing fields and tennis courts, three pools and a rifle range.

Its fees have increased by up to 19 per cent over the four-year period, with students now being charged $34,000 a year to attend the western Sydney institution.

The figures do not include the additional fees that many schools are increasingly charging for admission and yearly expenses, with International Grammar, Newington College, SCEGGS, and Knox Grammar charging parents well over $5000 on top of tuition.

The new data comes as another survey from the Australian Scholarships Group (ASG), released on Tuesday, shows that Sydney has held on to its title as the most expensive city for a private education in Australia.

The survey of 12,500 parents takes into account school fees, transport, uniforms, computers, excursions and sporting trips to determine the cost of education.

It found that for a child born in Sydney in 2017 the forecast cost of funding 12 years of private education was more than $575,000 – 18 per cent higher than the national average of $487,093.

Educating a child at a Catholic school would cost parents $250,862 over the same period, while sending a child to a public school would cost $75,080 in Sydney, slightly less than Melbourne's $77,371.

ASG CEO John Velegrinis said the cost of education has risen at 2½ times the rate of inflation over the past decade.

"If you have three children, the cost of educating them in Sydney's private education system could top $1.7 million," he said. "That's significantly more than the purchase price of the average family home."

But the Independent Schools Council of Australia has questioned the methodology of the survey, pointing out that only 12 per cent of independent schools in NSW cost more than $20,000 a year.

ASG, a business that helps people save for school fees, stands to profit from the outcomes of the research.

"Fees in independent schools vary greatly, with the majority of them much more affordable than modelling like ASG's suggests," said ISCA executive director Colette Colman.

Federal Education Minister Simon Birmingham said: "Every student deserves funding support, regardless of where they go to school in Australia.

"Ultimately, it is up to schools to justify fee increases to their parent communities, particularly where those increases go beyond the average inflation rate across the education sector."