Pupils say teachers and parents are not good at talking to them about sensitive issues like sexuality and are turning to magazines for help, a report finds.
Pupils want more talk about relationships
Inspectors for the schools watchdog, Ofsted, said magazines offered useful advice, even though they might be explicit and sexist.
And school nurses were providing a "valuable service" by offering contraception to pupils, Ofsted said.
Inspectors urged parents to put aside their embarrassment and talk openly.
The Ofsted report, based on 350 school inspections over the past five years, said pupils felt some of their parents lacked the knowledge and skills to talk to them directly about sensitive issues.
And girls aged 12 and 13 were now less likely to talk to their mothers about sensitive issues such as sex as traditional mother-daughter relationships changed.
The report said: "The increase in the number of magazines aimed at young men, while at times reinforcing sexist attitudes, has helped to redress the balance of advice available to young people.
"The range of topics and the explicitness in dealing with them have increased in many of the magazines read by young people."
The inspectors said extended schools, where nurses were on site to offer contraceptive advice, were helping reduce teenage pregnancies.
"School nurses can provide a valuable service, particularly in terms of providing emergency hormonal contraception and advising on other forms of contraception," the report said.
And it said where parents failed to set clear expectations for their children, schools became an important source of advice - hence the importance of good personal, social and health education (PSHE).
The report added: "Young people live in a world far removed from that which their parents experienced in their teens."
In its assessment of the PSHE offered to pupils in school, inspectors said lessons had improved over the past five years, but had "some way" to go.
They said teachers, governors and parents had not had sufficient support to handle these matters successfully.
Schools in England have to teach sex education, but PSHE is not statutory.
The report found poor lesson planning in PSHE contributed "substantially" to unsatisfactory teaching and pupils' needs had not always been identified clearly enough.
Inspectors also said transition arrangements for pupils moving from primary to secondary school were weak.
Ofsted called for better guidance for teachers, governors and parents to help them deal with sensitive matters within the PSHE curriculum.
Simon Blake, chief executive of Brook, the sexual health charity for young people, said: "Too many young people still report that they are not getting the information and support they need around sex and relationships either at home or at school.
"Making PSHE a compulsory part of the national curriculum would be the best way to drive up standards of teaching across the board and to ensure young people have the information and the skills they need to make informed choices about sexual health and to build healthy relationships."
Miriam Rosen, Ofsted director of education, said: "Personal, social and health education has made great strides over the last five years with improvements in teaching and learning.
"However, schools need to do more to ensure that they clearly understand pupils' needs and organise the curriculum accordingly.
"No matter how difficult it may be, parents and teachers have to discuss sensitive issues with their children and pupils to help them make the right choices as they grow up."
A spokesman for the Department for Education and Skills said: "We are taking steps to improve the support we give to parents to talk about sex and relationships, and we have made clear that local authorities and primary care trusts must make sure that they are providing young people with access to advice and contraception."
The department said it was improving the teaching of PSHE through "dedicated training programmes for teachers and community nurses" as well as the establishment of a new PSHE subject association.
The spokesman added: "We have made clear to schools that delivery of high quality PSHE is central to achieving the aims of the national curriculum, the five outcomes for children enshrined by the Every Child Matters agenda and for achieving National Healthy School Status."