England's education secretary has rejected MPs' calls to make sex-and-relationship education compulsory in all schools, infuriating campaigners.
Four key House of Commons committees wrote to Nicky Morgan last month, pressing for sex education to be made statutory in primaries and secondaries.
In response, Mrs Morgan now says the government "will continue" to keep the subject's status "under review".
But the National Aids Trust said it was "extremely disappointed".
The trust's chief executive Deborah Gold said the decision meant the subject "will continue to be delivered according to the whims of individual head teachers rather than the needs of young people".
Last month, the chairmen of the education, health, home affairs and business committees wrote to Mrs Morgan saying personal, social, health and economic education (PSHE), which includes sex education, was a "crucial part of preparing young people for life".
"It can provide them with the knowledge and confidence to make decisions which affect their health, wellbeing and relationships, now and in the future," said the joint letter.
"It can... help protect young people from abuse in many forms."
But Mrs Morgan said while she agreed PSHE was crucial, making it statutory "would do little to tackle the most pressing problems with the subject".
In a letter to Neil Carmichael, chairman of the Education Select Committee, she said these problems "are to do with the variable quality of its provision, as evidenced by Ofsted's finding that 40% of PSHE teaching is less than good".
"As such, while we will continue to keep the status PSHE in the curriculum under review, our immediate focus will be on improving the quality of PSHE teaching in our schools."
Under the national curriculum, sex-and-relationship education is compulsory from age 11 - but parents are allowed to withdraw their children from parts of it.
Mrs Morgan had previously failed to meet a deadline to respond to the Education Committee's call a year ago for the government to make a work plan for introducing age-appropriate PSHE and sex-and-relationships education (SRE) as statutory subjects in primary and secondary schools.
'Learning for life'
Lucy Emmerson, co-ordinator of the Sex Education Forum, described the subject as "every child's right".
"Yet the government has ignored the views of parents, teachers and pupils and failed to guarantee that all children, in all schools, get this vital learning for life," she said.
"SRE must begin in primary school and build year-on-year to enable young people to understand a wide spectrum of issues, including the difference between acceptable and abusive behaviour, consent and sexual health."
Dr Mary Bousted, general secretary of the Association of Teachers and Lecturers, said the decision was "short sighted".
"When report after report following the tragic sex abuse cases in Rotherham and Oxford point out that PSHE keeps children safe, how can Nicky Morgan refuse time and time again to make PSHE mandatory in all schools?" asked Dr Bousted.