Authorities are checking whether more pupils have been affected by the gaffe after Queensland ancient history students learnt they had been studying the wrong Roman emperor ahead of their final exam.
About 140 students are impacted after the number of schools across the state embroiled in the "extremely traumatic" mix-up rose from eight to nine on Wednesday.
"I'm very unhappy about the situation developing as it has, for the stress that it will have caused for everyone," Education Minister John-Paul Langbroek said.
Students were meant to study Julius Caesar but the affected pupils instead learnt about Augustus Caesar, according to the Queensland Curriculum and Assessment Authority.
Augustus was a focus of the 2024 exam, but this year the exam topic changed to Julius.
Students were told about the mix-up just days ahead of the final exam which is worth 25 per cent of their overall grade.
The curriculum authority said they were checking all 172 schools to confirm the number of students impacted.
Schools were notified of the topic for the ancient history external exam more than 12 months in advance.
But Mr Langbroek on Wednesday said "to the best of my knowledge" no other schools had been affected.
An investigation has been launched assessing the resources and planning provided by the authority to ensure there was no repeat of the gaffe.
"For all of us, as parents or students, who have been through situations like this it would be extremely traumatic," he said.
"I want to reassure these students and their parents and the teachers affected that we'll be making every investigation into how this happened."
The authority said on Tuesday schools involved in the bungle would submit an "illness and misadventure application" so students receive special consideration when their papers are marked.
"We are committed to ensuring every student receives fair and accurate results," it said.
20°C