In the end, the choice was easy. She left the public school system and enrolled at St Andrew's Cathedral School, one of 17 independent schools in NSW that gives year 11 and 12 students the choice of doing the IB instead of the HSC.

"I really like my old school, I just really wanted to do the IB," said Chiara, 17, now doing year 12.

Director-general of the IB program Siva Kumari is in Australia this week and will talk to the NSW government about allowing state schools to start offering the IB, as governments in Victoria, Queensland and South Australia have already done.

Dr Kumari said students should have the choice of doing the globally recognised program, even "if they don't have the option to pay the high cost of private school".

A spokesman for the NSW Department of Education would not comment on whether there were any plans to allow state school students to take the IB.

"No NSW public schools undertake the International Baccalaureate," he said.

"Students in government schools undertake the world-class Higher School Certificate."

The IB is recognised by Australian and international universities and can be converted into an Australian Tertiary Admissions Rank (ATAR).

The two-year program requires year 11 and 12 students to take six subjects including English, maths, science, a second language and a humanities subject, complete a 4000-word essay, a philosophical "theory of knowledge" course and a community service component.

Chiara said global recognition and the breadth of the IB curriculum were both part of its appeal.

"I just liked the idea that it was so internationally recognised because it opened so many opportunities later on in life," she said.

"Also the fact that you do such a broad range of subjects opens up options in regards to courses as you have such a broad basis of knowledge."

About a third of year 11 students at St Andrew's chose the IB over the HSC this year, the biggest number since the school started offering the program in 2009.

Chiara said the school provided plenty of information on both options, and about half of her friends decided to do the IB.

"Ultimately it was our personal choice whether we thought the IB suited our learning style and whether we liked the way it was set," she said.

St Andrew's IB diploma co-ordinator Sharon Munro, who led the school's introduction of the program, said the aim was to give students more choice.

"It's nice to be able to build choice into the curriculum and for kids to be able to choose based on their strengths," Ms Munro said.

"So if they're students who really just want to do a lot of humanities, they can do that in the HSC."

The head of the school, John Collier, said the IB and the HSC "are different and they're both high quality".

"The IB offers some things the HSC doesn't," Dr Collier said. "It's essentially a pre-university course aiming to prepare students. The learning techniques emphasise tertiary styles with independent learning and research."

Dr Kumari said the IB was "a fair system" because it was based on a student's individual mark instead of a scaled rank.

"In life, when you leave school, nobody is marking you against your colleague ... that's our belief in learning as well," she said.

In 2015, St Andrew's also implemented the IB middle years program, which is a teaching and learning framework for years 7 to 10 that can be incorporated into the local curriculum.

Five schools in NSW and 46 schools across Australia have introduced the middle years program, and 16 NSW schools and 121 schools across the country teach the similar primary years program.