The Speaking Out for Autism Spectrum Disorder group has expressed its anger at Ms Burch's treatment of the case as an "isolated incident".

In a letter penned by chairman Bob Buckley, the group has accused the ACT government of fixating on lessening damage to its image and cited concerns over the inquiry.

It is the third time a no confidence motion has been passed against the minister.

Telopea Park School declared a loss of confidence in Ms Burch in June over the removal of land from the school.

Before that, Canberra's government school teachers called on Chief Minister Andrew Barr to sack her as Education Minister, with the Australian Education Union passing a no-confidence motion in May.

The principal of the school where the cage was erected for a 10-year-old autistic student lost her job after the investigation found she was the sole instigator of the decision.

Mr Buckley said the matter was "not an isolated incident".

"The minister's attempts to portray it as such show little or no understanding of the level of systemic failure for autistic students in the ACT," Mr Buckley said.

"This attitude is unlikely to deliver improvements or reduce risk of abuse and neglect of autistic students in education or disability services in the ACT."

Mr Buckley said the goal of the letter was to draw attention to the plight of students with autism across Australia and create better education outcomes, including improved behavioural support in the classroom.

"The government has a long-standing policy of not doing that, through Disability ACT and the education department," he said.

"When this incident of the boy in the cage came up, for the minister to say it was a one-off incident, we threw our hands up in horror. It's entrenching the idea that we're going to see appalling outcomes for students with autism because we're not addressing the real issues."

Mr Buckley said the ACT government's goal during the cage incident was to minimise further damage to its image.

He also raised concerns about the expert panel appointed to investigate the use of the cage, citing a conflict of interest.

"The members of its expert panel are at least partially responsible for the design, staff training, operation and monitoring of existing education services in the ACT so, they have a substantial conflict of interest," he said.

"We are disappointed that the government is using the expert panel's existence as an excuse to avoid engagement with the ASD [autism spectrum disorder] community."

Mr Buckley said professional and behavioural scientists needed to be part of the solution.

"We need to get a clinician in who knows about autistic behaviour," he said.

Details about the $5195 cage, which was built by an external contractor, emerged earlier this month.

The two-metre-square structure was constructed out of blue metal pool fencing and included a self-closing latch and door.

When questioned by the Canberra Liberals during question time on Tuesday, Ms Burch said the construction of the cage was solely the responsibility of the school principal.

"It was no doubt a failing," she said. "The principal made this decision. She didn't take advice from the experts around her. She made a decision that was clearly [and] absolutely flawed."

Ms Burch said she did not see a draft version of the inquiry, which will not be released in full to the public.

"The investigation was done under the provisions of an EBA which is why the full report will not be released, but we recognised in public issues that the key findings of the matter needed to be put in the public space," she said.

In a further statement, Ms Burch said she has had many conversations with Mr Buckley over the years, in which he has made his position on these matters well known.

"On these issues I am taking the very best advice I can get, which is why in June I appointed the expert panel to review policy and practice for supporting and teaching students with complex needs and challenging behaviours," she said.

"The expert panel have engaged in extensive community consultation and are currently developing their report and recommendations to government."

Opposition education spokesman Steve Doszpot said it was up to Chief Minister Andrew Barr to revise Ms Burch's position in the government.

"A number of groups have now expressed no confidence in Joy Burch and its again up to Andrew Barr to reassess whether she should still be in cabinet," he said.