Education Minister Rob Stokes says he is "angry" that students at a regional NSW school have studied the wrong HSC mathematics course for the past seven months.

The students at Coonamble High School, in the state's central west, were reportedly taught General Mathematics 1, but had intended to study General Mathematics 2.

General Mathematics 2 is examined at the HSC and counts towards a student's Australian Tertiary Admission Rank (ATAR) while General Mathematics 1 is not.

The bungle is affecting five Year 11 students and two Year 12 students.

Students and their parents were reportedly distressed after being told they would have to learn the correct syllabus in just two months.

Mr Stokes said telling the students to cram for the exam over the next eight weeks, before and after school and on holidays, was "not acceptable".

"Another solution offered was that if they do not do well this year they can do it again next year — that's clearly a laughable solution," he told Radio 2GB.

"What the school has come up with in my view is not acceptable."

In a statement, Mr Stokes said he had instructed the maths inspector from the NSW Education Standards Authority (NESA) to go out to the school to determine the best course of action going forward.

Mr Stokes said he was "absolutely appalled" by what has occurred.

"This is not good enough ... my heart goes out to those students and their parents, I am angry on their behalf," he said.

"If this was my child I would be furious."

NSW Department of Education deputy secretary Murat Dizdar said the situation was "totally unacceptable".

"It simply should not have occurred and our full focus, attention and energy is to support the young people that have been affected by having the wrong course taught to them," he said.

"I appreciate it's a very stressful situation with our young people and their families and how we can cover the gaps in their learning that should not have been the case, we've taken swift action on that front."

Students were studying 'compressed curriculum'

In a statement, a Department of Education spokesman said the students were studying a "compressed curriculum", which was sometimes referred to as a "college-style" curriculum.

Students study both the preliminary (Year 11) and HSC (Year 12) course in the same year but only study half the usual number of subjects.

The spokesman said both mathematics courses had common areas of study.

"As soon as the executive principal identified that the correct mathematics course was not being taught, her immediate priority has been to provide comprehensive support to students," they said.

"Support will focus on each student's individual situation."

The spokesman said: "There will be a thorough investigation of the circumstances, including the roles of staff with responsibilities for teaching and HSC procedures."

"The school and the department is working actively with the NESA to support students and assist in its investigation."

Stephen Leonard's son, Cooper, is among the students who has been affected by the syllabus mix-up and said he believed it was a student who picked up on the error.

He said while his son was in Year 11, he would be under a large amount of pressure to catch up on the course work.

"Apparently it was only a student that was going through some stuff on the computer and picked up the error, which is quite concerning because the school itself didn't pick it up, one of the students did and then they notified the school, which in turn they notified us," Mr Leonard said.

"But it was very disheartening and a very, very concerning situation for all concerned.

"We need to come to some arrangement and we just feel like we've been left out. I think if they had the students' concerns foremost in their minds it wouldn't have been the approach they took."