Reddam House in Sydney's eastern suburbs surged up the HSC rankings last week to eighth spot, the only non-selective school in NSW to achieve a top 10 ranking, pipping top 10 stalwarts Sydney Girls and PLC, which between them have an extra 200 years of history on the Woollahra institution.

"Our owner, Graeme Crawford, prides himself on shaking things up," said Susie Britten, the school's head of English. "He would be incredibly proud to be competing with many other schools."

It's an unconventional result for an unconventional institution, which saw its ranking rise from 40th in 2010 to eighth last week.

Here teachers treat students more like colleagues and parents pay $29,000 to a school that was born out of a multinational operation that now spans eight campuses in the UK and South Africa.

Overseas the school's partner institutions also operate under the Reddam House brand but are run on a for-profit basis in the interests of both students and shareholders.

In Australia, where schools can not operate for-profit, its expanding early learning centre operation is the only part of the business that is run in a similar manner.

Last year it faced the Fair Work Commission over allegations that it had not paid some of its early learning staff overtime, penalties or provided them with pay slips. The school has since negotiated new enterprise agreements to cover its early learning staff.

Controversy with some of its employees has not dented parental demand for 900 student school which earned $3.4 million in government funding last year.

"On the back of some very good HSC results over the past four years our enrolments have gone off the charts," said Principal David Pitcairn.

This year the school outperformed all but the state's top school for 21 years running, James Ruse Agricultural High, across the higher-level English courses, while across all subjects 50 per cent of every exam taken by students scored 90 per cent or above.

HSC student Lily Speiser said tailored tutoring at the school pushed the former straggler to the top of her class.

"I was just an average student at my old school," she said. "They have this great philosophy at Reddam, they can take average students and expand their minds by working together."

The 17-year-old Bronte resident said the school emphasised collaboration over competition with students being encouraged to set up Facebook pages to share notes.

"I bounced off all of my peers especially with my English class, and that's where I succeeded the most," she said.

Lily's teacher, Ms Britten, said the school had encouraged students to abandon pre-prepared responses for their HSC.

"Four years ago we made a conscious choice to very deliberately steer our students away from that," she said.

"The pre-prepared essay is absolutely defunct. Thank goodness it's had its day and it's well and truly over."

Mr Pitcairn, who moved from one of the for-profit Reddam's based in Cape Town to run the Sydney school, said the school had separate business operations to the multi-national corporation.

"It is owned by an individual but the model remains the same as any other school in NSW," he said.

"The success of the school is down to the teachers relationship with the students," he said. "The students feel like they are working in a team."