Jon Slater reports
Many schools are failing in their legal duty to give pupils a proper education about sex and other health and social issues, according to the chief inspector.
David Bell said the quality of such lessons was frequently poor and some schools did not teach the subjects at all.
A shortage of specialist teachers and lack of time devoted to personal, social and health education (PSHE) meant young people were left ill-prepared for life after leaving school, he said.
"High-quality personal, social and health education is vital to young people's development, in and out of the classroom," said Mr Bell. "It is important that schools and parents take this role seriously to ensure our young people are prepared for the opportunities, responsibilities and experiences they will face."
Mr Bell's comments follow his criticism last week of citizenship teaching in secondaries and attack on some private Muslim schools.
He said schools had done little to improve PSHE since a critical report from the Office for Standards in Education in 2002 found that lessons taken by non-specialists were twice as likely to be unsatisfactory. This week's findings show that is still the case.
The Government responded by promising schools new material to help teachers assess pupils' progress in the subject, but, contrary to reports, pupils will not sit written papers at 11, 14 and 16.
A spokesman for the Department for Education and Skills said: "There is no question of pupils having to 'sit tests' in sex studies."
All secondary schools are required to teach pupils PSHE as part of the national curriculum.
Ofsted's latest report is based on a survey of more than 60 secondaries and inspection evidence from more than 100 others.
It found that some headteachers see the personal and social development of pupils as solely a matter for their parents, with some schools refusing to set aside separate curriculum time.
Many make PSHE the responsibility of untrained form teachers, and the introduction of citizenship lessons has squeezed the time available for PSHE in many schools.
Areas such as mental health, parenting, education and financial awareness are being neglected in many schools.
Mr Bell said: "I do not condone any schools deciding not to teach PSHE.
Schools need to ensure that those teaching the subject have the skills and support they need to deliver a first-class programme of lessons."
A DfES spokesman said that more than 5,000 teachers would be trained during the next two years.
Materials to help teachers with "informal assessment" of pupils' progress are being developed by the Qualifications and Curriculum Authority.
Anne Weyman, Family Planning Association chief executive, said: "It is iniquitous that provision of PSHE varies so widely, and disgraceful that in some schools it is not taught at all.
"The losers in the long run are not just young people but society at large and the NHS, which picks up the bill in terms of high rates of unplanned pregnancies and sexually transmitted infections."
She called on the Government to extend compulsory sex and relationships education to primary pupils.
Personal, Social and Health Education in Secondary Schools is available from www.ofsted.gov.uk
A GOOD PSHE TEACHER...
* has excellent subject knowledge
* the ability to encourage children to express their views and feelings
* has high expectations of pupils, taking their prior experience into account
* can promote respect for the views of others
* can use of group work, role play and whole-class discussion
* runs well-planned, structured lessons with opportunities to assess pupils' progress