Children will learn about parts of the body, the facts of life and puberty in primary school. At secondary school, they will be taught about pregnancy, contraception, HIV and homosexual relationships, it was disclosed.
All mothers and fathers will be able to keep children out on moral and religious grounds but will lose the right of withdraw when they turn 15. The ruling will affect 600,000 pupils a year.
The controversial move is designed to ensure pupils get at least 12 months of sex education before finishing compulsory schooling.
But parents’ groups said the decision risked “infringing parents’ rights” and claimed the Government was attempting to legislate in family life.
Faith schools will also be forced to teach all aspects of the new-style curriculum, including same-sex relationships, contraception and abortion, although ministers insisted they could stage lessons within the “tenets of their faith”.
Ed Balls, the Schools Secretary, said: “You can teach the promotion of marriage, you can teach that you shouldn't have sex outside of marriage, what you can't do is deny young people information about contraception outside of marriage.
“The same arises in homosexuality. Some faiths have a view about what in religious terms is right and wrong – what they can’t do though is not teach the importance of tolerance.”
Sex education will be introduced in 2011 as part of new compulsory lessons in personal, social, health and economic education (PSHE), the Government said.
Classes for five- to 16-year-olds will cover a range of lifestyle issues, including drugs, personal finance and first aid.
PSHE was introduced by Labour in 2000 but has not been part of the National Curriculum, allowing schools to drop it altogether. Ofsted said provision was “patchy” across England.
In the past, parents have been able to withdraw children from the sex education element of PSHE. Mr Balls said a “very small minority” of families exercised the power.
Government research published on Thursday suggested four in five parents wanted children to be given sex education, but almost a third insisted they should have the option to withdraw from lessons at any age.
But the Government said the right to opt out would be removed when children turned 15. It follows a review of the existing rules by Sir Alasdair MacDonald, head of Morpeth School in east London.
“This means that every young person will receive at least one year of [sex education] before their 16th birthday,” said Mr Balls.
Margaret Morrissey, from campaign group Parents Outloud, condemned ministers for “infringing parents' rights”.
Paul Tully, general secretary of the Society for the Protection of Unborn Children, said: “The government is removing the right of parents to protect their children from the explicit promotion of abortion and sexual health interventions in the latter stages. This will be exploited to pressure more schools to deliver government-style sexual health interventions. In recent years, these have been characterised by obscene and lurid presentations.”
But Chris Keates, general secretary of the NASUWT teachers’ union, said: “Allowing parents to withdraw their child from sex and relationship lessons up to the age of 15 does not sit well with a statutory entitlement.
“If it is important enough to be a statutory provision then it is important enough for every child to receive it. This is the only part of the National Curriculum from which parents have a right of withdrawal.”