Parents at the school publicly expressed their anger on Wednesday at a lack of information over the March incident, in which a student with autism was confined in a cage intended to be a withdrawal space.

In response to frustration at the lack of answers from an inquiry established after the incident was made public, more than 10 weeks ago, Ms Burch set up a hotline on Wednesday for concerned parents to call.

She defended the lack of information given to parents as necessary to protect the identity of the family involved.

"If you go and start to identify the broader school community, you identify the school, you identify the staff involved, you identify the family. And at all costs, I will maintain the privacy and the welfare of that family."

There have been reports of bitter divisions emerging within the school. The Canberra Times understands there was initial acceptance from some that a caged withdrawal space was a practical solution to separate the autistic student from classmates during moments of extreme behaviour.

ACT Opposition Education spokesman Steve Doszpot said parents and students were anxious and lacked support and information.

"There is no doubt that the students and parents have been impacted by the uncertainty surrounding this issue. Nobody is asking the minister to divulge information that will impact on the inquiry but she needs to talk to the school community about how they are feeling and what is troubling them."

He increased pressure on ACT Education Minister Joy Burch to expedite the inquiry into how the school came to erect the cage – made out of pool fencing – and who approved the decision.

In an Assembly estimates hearing on Tuesday, Mr Doszpot grilled bureaucrats in Shared Services about the 10-week delay in completing the inquiry. He was initially told key witnesses were on leave and the Australian Education Union had become involved, with the Hansard later corrected to say the delay was due to the complexity of the issues.

The AEU's ACT secretary, Glenn Fowler, said the union had invested considerable energy in supporting staff at the school.

"We have been involved from the start to ensure due process and procedural fairness are upheld during the investigation," Mr Fowler said.

The union is representing key staff.

Mr Fowler believed Ms Burch's initial response to the cage revelations had been unrealistic. "The minister's initial response heightened expectations around timelines for a matter that was potentially very challenging and complex," he said.

"One needs to be careful and circumspect in matters that may appear simple but rarely are."

Mr Boulter said it was "tremendously unsettling" for the school community.

"While we understand the need for privacy, the whole school community knows that they are the impacted school and it is in the interests of openness and transparency that this community is supported and cared for," he said.

- with Kirsten Lawson