One in three allow Bible lessons ... and some don't know what pupils are being taught.
One in three state primary and intermediate schools teaches religious instruction, according to a survey which has triggered a debate over what children are being taught - and the value of it.
The survey, sent to more than 1800 schools, reveals 578 have religious instruction classes.
Of these, 56 say they do not know the content of those lessons.
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Rationalist David Hines has created a public database on schools and their system of religious instruction. He believes religion should be separated from education because it divides students based on their parents' beliefs.
But the organisations teaching the programmes say they are upfront about teaching Christianity and the content of the voluntary lessons.
By law, state schools are secular, but can choose to "close" during school hours for half an hour of religious lessons each week.
Mr Hines said he started his survey of state schools after realising many parents were in the dark about what their children were being taught.
"It [religious instruction] is legal, but the schools shouldn't be doing it ... it means the whole school has to split along the lines of what their parents believe."
Using the Official Information Act, he questioned every state school that taught up to a Year 8 level.
Twelve schools did not know which organisations were running their religious instruction programmes, Mr Hines said, and 56 did not know what was being taught.
Mr Hines said the Connect programme, used by 57 schools, was the most evangelistic, and its leaders' handbook described how to introduce children to an appropriate church group.
Gail Hunter of Christian Education Publications, the New Zealand supplier for Connect, said the programme taught Christianity and was upfront about that.
Communities chose through school boards of trustees whether schools should offer lessons, and then parents decided whether their children would attend.
Jeff McClintock, who last year discovered his daughter, Violet, was left alone in a classroom "naughty corner" with a book after taking her out of Bible class, applauded Mr Hines' database.
The Red Beach Primary School parent said it was disappointing schools and the Government didn't have a system that could be used by religious and non-religious people to research educational facilities.
"I can't see any reason why schools can't be upfront and honest that they're running these courses and who's running them and all those details - that's the least they could do."
Mr McClintock said that since the story about his daughter was published in the Herald, a programme had been created for students who opted out of religious instruction.
Violet and four other pupils were now involved in a mentoring programme while others were in Bible class.
Churches Education Commission (CEC) chief executive Simon Greening said his organisation did not allow evangelism.
Pamphlets given to parents clearly stated the lessons taught Christianity.
"We are talking about faithful volunteers who have been going in there for years. CEC has been here since 1896."
Beachlands School principal Brian Gower said about 90 per cent of the Manukau school's 520 students attended the weekly 30-minute Bibles in Schools instruction run by the CEC.
The school was officially closed during that time, so other students could remain at home or attend a values programme run at the same time.
Mr Gower said parents were given direct links to information used in the sessions, and it was their choice what their child did.
The Bibles in Schools programme uses traditional Bible stories to reinforce basic Christian values.
Programmes cover reliability and trustworthiness, standing up for truth, self-discipline and self-control, doing one's best, consideration for others, unselfishness, respect and good manners, respect for rules, and understanding and acceptance of cultural differences.
"We put it out there and provide links," said Mr Gower. "They are available to go online. And the person who oversees the programme always drops me in pamphlets and material.
"You always get the odd case where there will be a misunderstanding in the classroom and some offence taken, but that's rare."
Mr Hines' survey showed 62 schools have dropped religious instruction since 2011, mainly because of a lack of teaching volunteers and a decline in parent support.
In 2006, the Government said requiring students to "opt out" of religious activities could be seen as discriminatory, but it did not adopt an "opt in" proposal.