The NAPLAN results for more than 1 million children have been caught up in controversy as education heads raise the alarm that it may not be possible to compare scores across the country.

Key points: NAPLAN results delayed over concerns national data could be invalid

NAPLAN results delayed over concerns national data could be invalid State and territory education heads have raised concerns results are not comparable

State and territory education heads have raised concerns results are not comparable Parents and educators are waiting for results that are "sitting on the shelves"

The national assessment authority, ACARA, was due to publish a summary of the preliminary results today, but there is disagreement between some states and the authority over how scores should be publicly reported.

A confidential document seen by the ABC reveals ACARA has been canvassing options for how and when to report the results since June, and the implications of each one, including the "reputational risk" to the national testing body, NAPLAN and My School data.

The ABC understands no agreement was reached and several state department heads questioned whether data was statistically comparable between the new online tests and the pen-and-paper version after seeing their students' test scores.

The education bosses are meeting with ACARA in Canberra today to try and resolve the impasse and have been speaking out about the situation.

'As a parent, I'm angry'

Before the meeting in Canberra, Victorian Education Minister James Merlino said the ACARA management of the online tests had been "appalling".

"From a Victorian perspective, I'm extremely concerned that we are now in a position where the data may not be comparable … as a parent of children who participated in NAPLAN this year, I am angry," he said.

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Principals are also worried about the uncertainty, saying they are concerned the data will be delayed further.

"Parents are asking when the results are coming," said Julie Ross, the principal of Kogarah High School in Sydney's south.

"I have to throw my hands up and say 'look I'm sorry, I can't tell you.' There's a lot of disquiet."

NSW Education Department secretary Mark Scott said parents should not be worried about their child's individual results.

"The testing authority said you'll be able to compare the pen-and-paper results and the online results. They're now backing away from that a bit," he told ABC Sydney radio.

"But what we know for sure is that parents will get an accurate report on what their students have been able to do and what they haven't been able to do in NAPLAN this year.

"So as far as the reporting on an individual child is concerned, [it's] accurate, and hopefully those reports will be with parents soon.

"What we may not be able to do is compare, for example, system-wide performance from this year to last year or previous years, that's going to be a challenge in these transition years before everybody gets to NAPLAN online."

In Queensland, Education Minister Grace Grace said concerns over the comparability of data demonstrated why a review of NAPLAN was needed.

"Again I call on Minister Birmingham to support a comprehensive and national review of NAPLAN not just on reporting, which is currently underway," she said in a statement.

"It is important that we maintain the public's confidence in NAPLAN, along with the support of teachers, principals and the broader school communities."

Assurance online, paper tests comparable under question

About 200,000 children sat online tests this year, which were designed to be adaptive and extend brighter students by prompting them to answer more difficult questions.

ACARA consistently assured parents, schools and education ministers the different test results would be able to be accurately reported on a common scale.

ACARA chief Robert Randall said in an open letter to parents on the day of the test this year: "Regardless of whether your child takes NAPLAN online or on paper, the results will be comparable with those of other students and from previous years."

That assurance is now under question.

If it is decided that student NAPLAN results cannot be mapped against a nationally consistent mean, it would undermine the test's central purpose as a point-in-time check of student progress in literacy and numeracy against benchmarks.

Principal Julie Ross said parents were asking when NAPLAN results would be released. ( ABC News: Natasha Robinson )

Ms Ross said many principals had long been concerned about consistency between online and pen-and-paper test results.

"It's a bit like comparing apples and pears, I don't know how you can," she said.

She said if schools had to wait much longer for results, the data could be useless to teachers.

"The results are supposed to identify the areas of need now," Ms Ross said.

"We did the test in May. We're now in August. If we don't get the results soon we will moving into term four.

"Programs that we could be implementing now to address some of the issues in the students' learning are sitting on shelves."

Data 'may not be publicly accepted as comparable'

An August 2 meeting of the Australian Education Senior Officials Committee, which is made up of education department heads from each state and territory as well as ACARA, failed to reach resolution on how the results should be delivered to schools and subsequently publicly reported.

A document put before the committee revealed ACARA was compiling advice on whether NAPLAN data would be statistically comparable this year, despite its previous assurances it would.

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The curriculum authority acknowledged concerns that even if its advice said the results could be directly compared, the data "may not be publicly accepted as comparable".

The committee was presented with several options for the reporting of preliminary NAPLAN results: to report scores for paper and online tests in one dataset against a national mean as planned, to issue two separate summary reports, or not to issue a summary report at all.

The final option would carry "reputational risk to ACARA" and "increase doubts over data comparability", the document noted.

ACARA also noted concern that failing to report national data would be "likely to generate negative media and negative stakeholder comment on the reliability and validity of NAPLAN data".

It would also create a "negative perception of the validity and usefulness of NAPLAN results" and would be "inconsistent with ACARA's current communications and messaging that data are comparable".

In a statement to the ABC, ACARA said NAPLAN results were "usually provided to schools, parents and students from mid-August to mid-September, depending on each state and territory".

On Wednesday, ACARA released another statement denying there was a delay, but saying "extra attention has been given to reviewing the data and ensuring it is comparable with previous years and between online and paper test modes".

The authority said it was "preparing to release results shortly".