Ms Burch's office said all interviews had been concluded in the matter and the independent delegate – ACT deputy director-general Gary Rake – was finalising the report.

A spokesman said this final stage – of a senior public servant in an unrelated directorate analysing the findings – was required for any HR investigation.

Ms Burch said in June she expected the inquiry would take about three weeks. It has now been 16 weeks since it was first called as a matter of urgency after Ms Burch announced that a cage had been discovered in a Canberra primary school as a withdrawal space for the 10-year-old boy with autism.

Opposition education spokesman Steve Doszpot said the length of time it had taken to get to the bottom of the matter was unacceptable and had been destabilising for the school community involved.

The principal has been moved to an administrative role within the Education Directorate pending the review's outcome.

"Minister Burch apologised that her initial claim in April that the inquiry would be swift had not been met, but assured an Assembly Committee that the report would be available in two to three weeks. Six weeks have passed and nothing has come from the minister – not an explanation, not an apology, nothing," Mr Doszpot said.

"Parents are still objecting to being kept in the dark about much of the issue, including whether the removal of the principal was a temporary or permanent arrangement, who authorised the cage structure and how on earth it was built in a Canberra classroom."

He also noted an opposition freedom-of-information request had been largely blocked "with many departmental emails remaining secret. Even the terms of reference have not been made public".

Ms Burch's spokesman noted "the privacy of the student and the family are of the utmost importance".

Australian Education Union ACT secretary Glenn Fowler said "arbitrary deadlines have been unhelpful as they have no bearing on the agreed procedures that relate to this matter".

"Of course, all parties are interested in this matter being concluded as swiftly as possible but not at the expense of natural justice and the most thorough of investigations," Mr Fowler said.

Meanwhile, submissions for the Shaddock review into ACT education services for students with complex needs are due at the end of this week.

Mr Fowler said the review "provides the profession with a rare opportunity to be consulted in depth about an increasingly complex environment where there is great expectation of teachers and school leaders but not always the resources required for them to do this challenging and crucial work".