God has been pulled from the classrooms of dozens of state schools in the past two years, as experts call for children to be taught about a wider range of faiths and values.

More than 50 state schools have cancelled Bible-based education in school hours since 2011, with a lack of teaching volunteers and decline in parental support cited as the main reasons.

Rationalist David Hines has questioned state schools about their religious instruction programmes under the Official Information Act, and plans to create a public database of the findings.

A member of the Secular Education Network, Hines is against religion being taught in publicly funded schools.

The initial results from his survey show that 56 schools have stopped religious education since 2011. Of the 1429 schools that responded, 38 per cent have held some kind of religious instruction during school hours this year.

Another 58 per cent either had no religious instruction, or held it at lunchtime or after school. The remaining 4 per cent had not yet decided.

Some schools said increasing numbers of children were being pulled from classes, while others couldn't fit the Bible in Schools programme into their stretched curriculums.

Christchurch's Sheffield Contributing School principal Simon Moriarty said it stopped religious education because it did not need the Bible to teach a values-based curriculum.

"Parents didn't feel strongly that there was a need for religious instruction here at the school. They saw that there were a lot of options for them in the local community."

The survey showed that not all religious instruction was Christian, with at least one Auckland school offering children tuition in Islam.

Owairaka School principal Diana Tregoweth said the multicultural school had held Islam lessons alongside Christian teachings until recently, when the tutor left for a fulltime job.

"Now we've just got the ordinary Bible, but we're sort of reviewing that too because we do have lots of [pupils of] other religions here."

Whether one religion should be taught to the exclusion of others would be debated in the upcoming review, she said.

A Sunday Star-Times reader poll last year found 49 per cent of respondents against religious studies in primary schools, and 43 per cent were in favour. The rest were undecided.

Hines found the main provider of religious education was the Churches Education Commission, which works with 712 schools and represents 16 denominations. The next biggest provider was local churches, including Jehovah's Witnesses and Baptists.

He plans to contact each of the 20 religious organisations listed by schools as providing their programme, and to provide summaries of their beliefs.

"That, I hope, will show what concerned parents want to know: are their children being raised by bona fide teachers of universally shared values, or are they receiving biased programmes, unsuited for public schools?"

Churches Education Commission chief executive Simon Greening said its programme used the Bible to teach morals, and opting in was up to the school's board of trustees.

"There's no doubt, and we're up front about this, that we teach Bible studies. But the idea is to connect Bible studies with values."

But Victoria University religious studies professor Paul Morris says a wider approach is needed, and it is "vitally important" children learn about all faiths - particularly in today's global environment.

"If we want to understand the world we live in, then the understanding of religion isn't an option. It's a necessity."

At the last census, about half of respondents said they were Christian. Nearly a third had no religion.