The Victorian Tertiary Admissions Centre contacted Carey Baptist Grammar School and Wesley College this week and asked them to remove data that conflated the scores of both their VCE and International Baccalaureate (IB) students.

On Wednesday it wrote to every Victorian school offering the IB alternative to VCE to warn them against publishing combined results from the two certificates.

Schools had been equating VCE study scores of 40 or more with the top IB subject scores of 6 or 7.

Achieving a VCE study score of 40 or more (out of a possible 50) places students in the top 9 per cent across Victoria.

But according to VTAC, a third of IB students achieve a score of 6 or 7.

“To consider an IB study score of 6 as equivalent to a VCE study score of 40 would be an inaccurate assumption,” VTAC spokeswoman Suzanne Connelly said.

“VTAC has written to all Victorian IB schools advising them of the outcomes of this analysis. Schools publishing any conflated tables have been asked to remove them from their websites.”

Ms Connelly said VTAC believed the data was published in good faith, and there was no deliberate attempt to misrepresent it.

The IB Heads Association of Victoria and Tasmania said it adopted a policy in 2015 that saw scores of 6 or 7 in Standard and Higher level IB subjects ranked as equivalent to a VCE score of 40 or more.

"In recent days, member schools have alerted the association that VTAC is uncomfortable with this approach," the association's chairman David Fitzgerald said.

"As such, the association will, as a priority, write to member schools advising them that the matter is being reviewed."

Carey reported on its website that when VCE and IB results were combined, 25.8 per cent of study scores were 40 or above.

When IB results are excluded, official data from the Victorian Curriculum and Assessment Authority shows that 10.5 per cent of Carey students achieved a study score of 40 or above in the VCE in 2017.

The school achieved an average IB score of 36.2, which equates to an ATAR of 94.85.

Meanwhile, Wesley stated on its website that 29 per cent of its Year 12 class achieved study scores of 40 or above in 2017 when its IB and VCE results were combined.

When IB results are excluded, Wesley achieved 12.1 per cent of study scores of 40 or more at its Melbourne campus and 7.9 per cent at its Glen Waverley campus.

Its IB students achieved a median ATAR of 93.45.

Both schools have a large proportion of students who graduate with the IB.

Carey principal Philip Grutzner said his school combined its VCE and IB scores to provide the community with information that was unavailable in league tables published in the media.

“The IB program and its assessment are not widely understood and combining results gives a better indication of how IB study scores fit into our overall Year 12 results,” he said.

He said the school had published the data in good faith and had removed it following VTAC's request.

Wesley College principal Helen Drennen said her school had published the data to celebrate the achievements of all Year 12 students. "This data is aggregated in good faith to provide a clear and accurate representation of the cohort as a whole," she said.

She said the school had removed the information from its website, but had proposed changes to its wording to VTAC.

A teacher raised concerns about the conflated data with Carey and Wesley earlier this year before contacting VTAC, the VCAA and Education Minister James Merlino.

The man, who did not want to be named, said the schools had presented false information that inflated their results.

“Parents should have access to accurate information," he said.

Seventeen Victorian schools offer the senior IB qualification. Of these, 15 are non-government schools and two are government.

While there is no definitive mapping from individual IB studies to VCE studies, VTAC creates notional ATARs for IB students.

Deakin University education lecturer Dr Emma Rowe said schools wanted to communicate with parents in a language they understood.

“VCE is the dominant language,” she said. “If you want to put that big heading on your website or the boards in front of your school, you want to put it in the most dominant market speech.”

She said in a competitive market, schools had to convince parents that it was worth spending money at their school.

“They are conflating their test scores to get their customers through the door,” she said.