A high school teacher in Australia who assigned her class to plan a terrorist attack that would kill as many innocent people as possible had no intent to promote terrorism, the school principal said.

The Year 10 students at Kalgoorlie-Boulder Community High School in the state of Western Australia were given the assignment last week in a class on contemporary conflict and terrorism.

They were asked to pretend they were terrorists making a political statement by releasing a chemical or biological agent on "an unsuspecting Australian community", according to a copy of the assignment received by the West Australian newspaper.

The task included choosing the best time to attack and explaining their choice of victims and what effects the attack would have on a human body.

"Your goal is to kill the MOST innocent civilians in order to get your message across," the assignment read.

Principal Terry Martino said he withdrew the assignment as soon as he heard of it.

"The teacher, who is relatively inexperienced, made a well-intentioned but misguided attempt to engage the students in an assignment on contemporary conflict and how beliefs and values influence the behaviours and motives of individuals," Mr Martino said in comments provided by the state Education Department.

Mr Martino said the highly regarded teacher was not promoting terrorism but just made a mistake. He said she was remorseful and understood the topic was inappropriate.

The school declined to identify the teacher, citing her privacy, and her name also was not given in the newspaper report.

The Education Department's director requested a full report on the incident, which was revealed in a front-page article in the West Australian newspaper today.

Student Sarah Gilbert, 15, told the newspaper she was horrified by the assignment.

"I was shocked and quite offended," she said. "I'm offended that it's Australia but I'm disgusted because it doesn't matter where it is, it's still not something you ask someone to do or think about. ... There is a difference between being a terrorist and learning about terrorism."

Sarah - whose mother lost a relative in the 2002 Bali bombings - wrote a letter to her teacher refusing to do the assignment.

"Even though it may seem petty, to me my beliefs are more important than an A stating I am smart," Sarah wrote. A copy of her letter was published by the newspaper.