All children from the age of four will be taught about safe and healthy relationships, Education Secretary Justine Greening said.
Children will also be taught, at an appropriate age, about sex. But parents will still have the right to withdraw their children from these classes.
Until now, sex education has been compulsory only in council-run schools.
Since academies and free schools are not under local authority control, they do not have to follow the national curriculum and have not been obliged to teach sex and relationships education (SRE).
In practice, the vast majority do teach the subject – the government’s announcement will mean all schools across the system will be bound by the same obligation.
Age-appropriate lessons will have particular emphasis on what constitutes healthy relationships, as well as the dangers of sexting, online pornography and sexual harassment.
In primary schools, the focus would be on building healthy relationships and staying safe, the Department for Education (DfE) said, while in secondary school it would focus on sex as well as relationships.
The government will hold discussions on what should be taught to children, and at what age, and there will be a public consultation later this year.
Pupils could be taught the new curriculum from September 2019, the DfE said.
In a written statement, Ms Greening said: “The statutory guidance for SRE was introduced in 2000 and is becoming increasingly outdated.
“It fails to address risks to children that have grown in prevalence over the last 17 years, including cyberbullying, sexting and staying safe online.
“Parents will continue to have a right to withdraw their children from sex education.
“Schools will have flexibility over how they deliver these subjects, so they can develop an integrated approach that is sensitive to the needs of the local community; and, as now, faith schools will continue to be able to teach in accordance with the tenets of their faith.”
The news was welcomed by the Local Government Association, which has been campaigning for compulsory sex education in all schools.
Izzi Seccombe, chairman of the association’s community wellbeing board, said: “The lack of compulsory SRE in secondary academies and free schools is storing up problems for later on in life, creating a ticking sexual health time bomb, as we are seeing in those who have recently left school.
“We believe that making SRE compulsory in all secondary schools, not just council-maintained ones, could make a real difference in reversing this trend, by preparing pupils for adulthood and enabling them to better take care of themselves and future partners.”
But critics fear the announcement weakens the influence of parents.
Safe at School Campaign described the announcement as a “tragedy”.
National co-ordinator Antonia Tully said: “Parents will be absolutely powerless to protect their children from presentations of sexual activity, which we know is part of many sex education teaching resources for primary school children.
“The state simply cannot safeguard children in the same way that parents can. This proposal is sending a huge message to parents that they are unfit to teach their own children about sex.”
Russell Hobby, general secretary of school leaders’ union NAHT, said age-appropriate SRE would prepare young people for the challenges they faced.
“It is so important for young people to be taught about appropriate relationships, and the duties set out today bring that one step closer.”
Malcolm Trobe, interim general secretary of the Association of School and College Leaders, urged the government to give schools the freedom to be innovative and flexible in the way they approached the subject.
“We do not believe it is necessary for the government to provide standardized frameworks or programmes of study, and we would urge ministers against being too prescriptive,” he said.
The Right Reverend Stephen Conway, the Church of England’s lead bishop on education, said he supported age-appropriate SRE.
“In an age when even primary school children are becoming exposed to online pornography – often by accident – and when practices such as sexting are becoming commonplace at a younger and younger age, we cannot simply advocate an approach like the three monkeys covering their eyes, ears and mouths, vowing to see, hear or speak no evil.
“If we want children to build resilience it is important to start young, teaching them about strong and healthy relationships.”
Ms Greening’s announcement follows a widespread campaign by charities, MPs and local authorities, calling for (SRE) to be made a statutory for all schools.
At the end of last year, the chairmen and women of five different Commons select committees called on Ms Greening to make SRE a statutory subject.
Elsewhere in the UK
SRE is part of the curriculum in Wales, but it is not currently compulsory.
The Welsh government says it expects young people to receive age-appropriate lessons in school, covering “all aspects of relationships, sexual health and well being issues”.
The subject is not compulsory in Scotland but new guidance was introduced in 2014. Schools and local authorities are responsible for deciding how to put the guidelines into practice.
In Northern Ireland, the Department of Education requires each school to have its own written policy on how it will address the delivery of relationship and sexuality education (RSE).
RSE must be delivered “in a sensitive manner which is appropriate to the age and understanding of pupils and the ethos of the school”.
England is one of the Countries which has stripped parents from Parental powers and responsibilities, and the powers have been given to the Social Services which is highly overwhelmed.
Teachers who have other sexual Orientations eg.Gays and Lesbians ,will have opportunities to introduce very young children to same sex relationships, which may be against the moral campuses,Faiths and standards of life of Parents and families.
The Parents should be equipped to train their Children based on their:Faiths, Moral stands and sexual orientation.
At the young age of 4 children are still learning how to brush their teeth, and discovering different types of foods and Cuisines , Indian, Chinese or African, trying to introduce these children to sex or relationships education despite the appropriateness of the Contents is immoral and a time bomb for England sexual and relationships behaviors as a Nation.
Staff Reporter and Agencies