The majority of fee-paying schools have backed an attack on the new curriculum, which they say has had a disastrous effect on learning. Topics including gender equality, parenting skills, climate change and Islamaphobia leave little room for traditional subjects, they say.
Instead, the schools want lessons to focus on core knowledge, including dates and key figures in history, spelling in English and times tables in maths.
Five main independent school associations, which represent 80 per cent of fee-paying schools, have all given their support to a new curriculum for their 500,000 three to 14-year-olds.
Michael Spinney, chairman of the Independent Association of Prep Schools, who announced the plan, said: "Increasingly, we live in an era where teaching and learning are sacrificed in favour of fashionable causes, often with disastrous effects upon standards of learning."
Mr Spinney, speaking at the annual Girls' Schools Association conference in Leeds, criticised the inclusion of the slave trade in history lessons as a way of addressing concerns over multiculturalism.
Another "classic example" of the problem with the curriculum was the decision to drop Winston Churchill from a list of historical figures to be studied, he said.
Independent schools do not have to follow the national curriculum, but the vast majority do so to prepare pupils for GCSE and A-levels.
Under government changes to the curriculum for 11- to 14-year-olds, teachers will be given greater freedom to choose what they teach.
A spokesman for the Department for Children, Schools and Families dismissed the criticisms.
The announcement came just hours after Lord Adonis, the schools minister, urged independent and state schools to work more closely together.
He said pound;4 million would be invested in the independentstate school partnerships scheme, so schools could work together on providing masterclasses for pupils and extra training for teachers.
Money would be given to clusters of schools, with the aim of getting more bright, but disadvantaged children into university.
The funding is the latest attempt by the Government to use private schools to close the attainment gap between rich and poor pupils and follows a call for independent schools to back academies.
Pat Langham, GSA president and co-chair of the independentstate school partnership scheme, welcomed the money. But earlier in the conference she said the idea that independent schools should "come to the rescue" of failing state schools was patronising and misguided.
Changes to the law mean that independent schools will have to prove they benefit the public if they are to retain their charitable status.
Some independent schools are already shifting money away from scholarships for the brightest pupils to means-tested bursaries, it was reported this week.
Meanwhile, another headteacher told the GSA conference that children should be allowed to "toboggan" down staircases and walk in the woods at night without a torch to help them learn about risk.
Robert McKenzie Johnston, head of Queen Mary's School in Thirsk, North Yorkshire, said: "If they learn for themselves what's sensible, they will make mistakes and get grazed knees and bruised noses. But it won't matter because they will learn what they can and cannot do."