Parents, teachers and students from across the state have told a parliamentary inquiry into home schooling they consider creationism, the belief that the universe was created by God, to be a valid scientific theory.

Representatives from the Home Education Support and Action Network, where the majority of members are Christian, said they believed creationism and evolution should be taught as equal theories. And the four teenagers who presented evidence to the committee on Friday said they believed creationism was a valid scientific theory.

At the hearing on Monday, the general manager of Australian Christian Home Schooling, Dr Terry Harding, said creationism was taught as part of science but accepted it was not a scientific theory.

"There would be some of it in the science section," he said. "We wouldn't say that's a scientific theory, but in the curriculum we would provide information as to the creation idea of origins and the evolutionary idea of origins."

He argued it was relevant to science because it related to the natural world and was part of a continuing scientific debate.

"But in terms of scientific methodology, which is based on observation, there was no one at the beginning, whether it was the big bang or a creation, and thus it's not scientific methodology," he said. "However, because it relates to the natural world and science relates to the natural world, it's relevant."

Fairfax Media reported in August that up to 10,000 students in NSW were home-schooled despite only 3238 being registered. Home schoolers are required to teach the full curriculum set by the Board of Studies, Teaching and Educational Standards NSW.

Several parents who spoke at the inquiry indicated they taught the theory of evolution, in addition to creationism, because it was prescribed by the NSW curriculum.

"We have a creation point of view. We are Christians and we teach according to our understanding of the Bible," Marianne Vanderkolk, a parent and home-school teacher, said. She said she taught her children the universe was "6000 to 10,000 years old".

A spokesman from BOSTES said there was flexibility in the curriculum in terms of the content taught and degrees of emphasis.

"While creationism and intelligent design are not part of the BOSTES syllabuses and are not tested or assessed for the HSC, they can be taught," he said.

"Schools that choose to teach creationism, outside of their BOSTES based science programs do so in addition to and not part of BOSTES syllabuses."

Greens NSW MP John Kaye, the committee's deputy chairman, said he was concerned a cohort of home-schooled children would not be able to tell the difference between religious belief and scientific theory.

"Their ignorance will impose costs not only on themselves but also on the society they will grow up in," he said