The High Court will rule on whether the Government has "skewed" the teaching of religion in schools by leaving out "non-religious world views" from the new religious studies GCSE.
Three families, supported by the British Humanist Association, brought the legal challenge - claiming Education Secretary Nicky Morgan has taken an unlawful approach and is failing to reflect the pluralistic nature of the UK.
Changes to RS GCSE subject content were announced last February, leading to complaints over the way priority has been given to religious views - in particular Buddhism, Christianity, Catholic Christianity, Hinduism, Islam, Judaism and Sikhism.
David Wolfe QC, for the families, submitted to Mr Justice Warby at a recent hearing in London that the curriculum was being skewed, and there was widespread concern "about the secretary of state's failure to comply with her duty of neutrality and impartiality as between religious and other beliefs".
Earlier this year, the former Archbishop of Canterbury Rowan Williams was among 28 religious leaders who urged the Government to rethink the current plans to leave out humanism in the new qualification.
Lawyers for the Education Secretary said neither domestic law nor the European Convention on Human Rights require equal consideration to be given to religious and non-religious views in the curriculum.
They argued that, although some schools rely on the RS GCSE to discharge their duty to provide religious education at key stage 4 for 14-16 year olds, provision has been made for non-religious beliefs to be studied and what is in a school's curriculum is a matter "for local determination" by individual school authorities.
The families seeking judicial review include one from Cumbria and one from Kent and cannot be identified.
The third family is Kate Bielby, of Frome, Somerset, and her daughter, Daisy.
Ms Bielby said before the hearing: "I completely recognise the importance of children learning about the different religions, especially in our increasingly diverse society.
"What I object to is the lack of parity between religious beliefs and non-religious worldviews in the school curriculum, which in the eyes of children may well lead to the belief that religion, in whatever form, has a monopoly on truth and on morality."
She added: "This is not accurate, it reflects neither the views of the population nor the traditions of the country, and we shouldn't be encouraging our children to believe it."
BHA chief executive Andrew Copson said: "The law is clear that when teaching about religions and beliefs, schools should follow a broad and balanced syllabus which includes both religious and non-religious world views like humanism on an equal footing.
"The religious studies GCSE is therefore incompatible with the rights of non-religious parents and the entitlement of young people to an education that does not indoctrinate them, even by omission."