All children from the age of four will be taught about safe and healthy relationships and children in secondary schools will be given age-appropriate lessons about sex.
The move follows months of campaigning from MPs and charity groups who successfully argued that the current curriculum is years out of date and does not reflect the dangers faced by young people today.
Until now, schools that are not under local authority control have not been obligated to include sex and relationships within their teaching, and those that are need only include biology.
The Government’s announcement will mean all schools across England are now bound by the same obligation and include lessons on the dangers of online pornography, sexting and sexual harassment.
In a written statement, Ms Greening said statutory guidance for Relationships and Sex Education (SRE) was introduced in 2000 and is becoming “increasingly outdated”.
“It fails to address risks to children which have grown in prevalence in recent years, including online pornography, sexting and staying safe online,” she said. “As a result now is the right time to address these issues.”
The Department for Education will work with teachers, parents and safeguarding experts to develop age-appropriate content for all key stages.
Amendments to the Children and Social Work Bill will also allow the Government to make regulations requiring PSHE to be taught in all schools in England in the future, ensuring all primary, secondary, maintained and academy schools are bound by law.
Parents will continue to have the right to withdraw their children from sex education classes, however, and schools are given flexibility over how they deliver the subjects.
Faith schools will also be able to continue to teach “in accordance with the tenets of their faith”, although it remains unclear how this will be monitored.
The move has been welcomed by education leaders and campaigners, including Refuge, who said the landmark decision could help reduce domestic violence for future generations.
Sandra Horley, Chief Executive of the charity said: “SRE provides young people with the knowledge they need to develop relationships based on equality and respect, how to recognise domestic violence, and how to seek support when needed.
“We believe domestic violence incidences will fall if the next generation is equipped with this knowledge from a young age. Today is a great first step towards a better and safer future for young people.”
Ian Green, Chief Executive of HIV and sexual health charity The Terrence Higgins Trust, agreed it was a decision that had the potential to change young lives for generations to come.
“Until now, there has been nothing in place to ensure we are safeguarding all young people by discussing issues such as consent, abuse and what a healthy relationship looks like from a young age, in a safe environment and with trained professionals,” he said.
“However, in order to fully address the sexual and mental health crisis among young people, we will need to ensure that any legislation around SRE has a strong emphasis on neglected topics such as sexual health and on LGBT relationships, in order to tackle high rates of STIs among young people and ongoing homophobia in our school corridors.”
The Safe at School Campaign described the announcement as a “tragedy”, however, claiming parents would be “absolutely powerless to protect their children from presentations of sexual activity”.
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 standardised frameworks or programmes of study, and we would urge ministers against being too prescriptive,” he said.
A YouGov poll from Barnardo’s children’s charity earlier this year found 74 per cent of 11-15 year-olds said they would feel safer if they were taught about sex and relationships in school.
Some 94 per cent said they agreed it was important for them to understand the risks and dangers of being online in order to stay safe.
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