Up to 20 schools will take part in the trial after ethics provider Primary Ethics appealed to the department when schools did not respond to invitation letters following advice from the NSW Secondary Principals Council.

At a meeting between the department, Primary Ethics and the Secondary Principals Council last week the department confirmed that Primary Ethics, as the approved provider of ethics classes in NSW, has the right to offer ethics classes in high schools as an alternative to mandatory scripture classes.

The move by Primary Ethics, which runs ethics classes to 40,000 kindergarten to year 6 students in more than 500 state primary schools, will reignite tension in the secondary sphere after the Secondary Principals Council campaigned to scrap mandatory scripture in high schools following release of an independent review in 2017.

The review of Special Religious Education (SRE) and Special Education in Ethics (SEE) fell short of recommending mandatory scripture in high schools be scrapped, but a recommendation that students who opt out of scripture should be able to do regular school work during scripture was rejected by the NSW Government.

Under current legislation no "academic or formal school activities" can occur during scripture time for students who do not attend scripture. Parents who objected to their children being forced to watch films or wait while scripture sessions ended were a driving force behind the rise of ethics lessons as an alternative for non-scripture students in state primary schools.

Recent audits by parent group Fairness in Religions in School (FIRIS) found less than 2 per cent of year 7 students at one Hunter high school attend scripture, but an accurate estimate of how many students attend across state primary and high schools is difficult because there is no central monitoring of scripture figures.

The NSW Government rejected a review recommendation for "accurate and regular monitoring data about the nature and extent of Special Religious Education in NSW Government schools".

A Department of Education spokesperson confirmed it was working with Primary Ethics on "the future delivery of Special Education in Ethics (SEE) in high schools" but referred questions to the Secondary Principals Council about correspondence on the ethics pilot between the council and individual high schools.

The council's acting president Craig Petersen said it had sent out "some clarification to schools" about its position there should be "no mandated Special Religious Education" in high schools, after individual schools received the Primary Ethics request to participate in a trial several months ago, and before it was aware Primary Ethics had made an "official approach" to the Department of Education.

"Until there was an endorsement principals needed to be aware of the Secondary Principals Council's position," Mr Petersen said.

The advice was based on mandatory SRE "creating a space" for the ethics provider to make the shift to high schools, and the council's view that SRE should be voluntary and not mandatory in the secondary sphere, Mr Petersen said.

"Schools might make a decision for SRE to run but it should be the school's decision, especially at the moment when there's so many demands on school time. Our position on ethics is pretty similar," he said.

A recent FIRIS audit that found the overwhelming majority of state high schools were failing to meet even minimum Department of Education guidelines on information to parents about scripture enrolment, approved scripture providers and material taught was not surprising, Mr Petersen said.

"In some schools you've got such small numbers taking part in SRE that it is possible people have overlooked making the most recent department changes because they prioritised other things," he said.

Department of Education training seminars in the most recent changes to procedures about how parents are informed of SRE and SEE, including that parents now "opt in" their children to SRE rather than "opt out", were poorly attended.

"I didn't do it myself," Mr Petersen said.

Issues for state secondary principals include that "the take-up rate of SRE in high schools is very low", there are often competing demands from competing religious groups and "sometimes it's the quality of people delivering the SRE", he said.

The overwhelming issue for secondary principals was "we're so pushed getting through the curriculum".

"The common feedback is that the curriculum's too crowded but it's a legislative requirement that SRE is mandatory. It's something people are very passionate about and it's highly emotive," he said.

"Noone wants to be the person who bans scripture from schools but under our current system SRE providers aren't happy and many schools aren't happy. The problem is where we're trying to force it across all schools."

Primary Ethics chief executive Evan Hannah said his organisation's move into secondary schools followed requests by parents and talks with a former education minister and shadow minister.

"We've had regular questions from parents who, on enrolment, have been asked what SRE they've wanted their child to do, and they've asked why ethics isn't offered in high school," Mr Hannah said.

"We're only interested in going to those schools where student have technically nothing else to do while scripture is on. We're writing a curriculum now for year 7 and we're seeking schools to express their interest to us."

Mr Hannah said the Department of Education had shown over recent times "a more overt approach in supporting our work of providing equity for parents who choose an alternative to SRE".

"We have a better relationship with the department, and we're grateful for that, after some years of struggle."