Children as young as five should be given lessons in sex and relationships, a health watchdog said today.
Good quality classes on sex, relationships and alcohol help youngsters to understand the risks and consequences of their actions and resist peer pressure, according to the National Institute for Health and Clinical Excellence (Nice).
Research shows that two-fifths of young people rate sex education in their school as poor or very poor, it said.
In draft guidance published today, Nice said that sex and relationships education is "more effective if it is introduced before young people first have sex".
It calls for youngsters to be given lessons which are "factually accurate, unbiased and non-judgmental", tailored to each age group, and take into account "cultural, faith and family" issues.
It means primary school pupils could start by learning about friendships and respecting others, the guidance says.
Plans for a new compulsory sex and relationships curriculum were contained in an education Bill put forward by Labour under the last Government.
But the proposals, which would have seen pupils taught about contraception and the importance of stable relationships, including civil partnerships, among other topics, were dropped from the Bill shortly after the general election was called following opposition from the Tories.
Nice's draft guidance says that pupils should receive sex education classes throughout their school careers - from primary school to early adulthood.
And parents should be told that the classes will help children understand their own development, and will not encourage youngsters to have sex earlier - a key concern of some family campaigners.
Parents and pupils should be involved in creating a curriculum for the topic, it says.
Gillian Leng, Nice deputy chief executive, said: "Starting personal, social, health and economic (PSHE) education early can help improve a child's ability to develop and sustain friendships, and understand the importance of valuing and having respect for others, building the foundation for later teaching about important subjects such as alcohol and sexual relationships."
Simon Blake, chief executive of sexual health charity Brook, and part of Nice's programme development group, said: "It's a myth that sex and relationships education encourages children to be more promiscuous or have sex at an early age. In fact, evidence demonstrates this type of education helps children and young people resist pressures to get involved in activities that might damage their health.
"Importantly, it helps them develop the skills to only have the sex they choose when they are able to enjoy and take responsibility for their personal relationships and sexual health."
Ministers are looking at sex and relationships education as part of a wider overhaul of the curriculum, the Department for Education said.Reuse content