TEACHERS will have a legal duty to encourage teenagers to delay engaging in sexual activity as part of a wide-ranging package of concessions made by the Government to family values campaigners as it plans to scrap Section 28.

What children must lean All children, from the last year of primary school onwards, should:  learn about the nature of marriage and its importance for family life and bringing up children. learn the significance of marriage and stable relationships as key building blocks of community and society. lean to respect themselves and others. be given accurate information for the purposes of enabling them to understand difference and of preventing and removing prejudice. be protected from inappropriate teaching and materials. Secondary pupils must also: learn to understand human sexuality learn the reasons for delaying sexual activity and the benefits to be gained from such delay. learn about obtaining appropriate advice on sexual health.

David Blunkett, the Education Secretary, will announce today that he intends to enshrine the value of marriage in law in a landmark decision on the Government's moral role in society. Schools will be required to teach about the nature of marriage and its importance for family life and bringing up children. They will be legally bound to tell their pupils "marriage and stable relationships" are the building blocks of society. 

Teachers will be banned from using "inappropriate" material in sex education classes - both homosexual and heterosexual. Secondary schools will also have a legal duty to encourage pupils to avoid early sexual activity. Mr Blunkett has agreed to table an amendment covering the commitments to the Learning and Skills Bill, now going through Parliament.

The compromise has infuriated other ministers. One said the clause would be "Section 28 plus" - more draconian than the original clause which stops local authorities promoting homosexuality. The Education Secretary will also publish new legally binding guidelines for schools on sex education which make clear that parents should be consulted about all lessons and have the right to take their children out of classes.

Although the guidelines do not specifically mention the promotion of homosexuality, they say: "Inappropriate images should not be used nor should explicit material not directly related to explanation." Sources said that all the homosexual literature attacked by family values campaigners would be covered by this clause. The amendment was finalised in agreement with church leaders in return for their support for the repeal of Section 28.

The concessions are likely to win over many of the peers who rejected the Government's attempt to scrap Section 28, part of the Local Government Act. Anglican bishops believe that the amendment means marriage is enshrined as the ideal model for society despite the recognition of the value of "stable relationships" of other kinds.

The guidance on sex education will emphasise that all teaching should be appropriate to the age of pupils. It will say that parents must be fully consulted about lessons and retain the right to take their children out of sex education classes. Schools will be advised to hold separate classes for boys and girls. 

Several Cabinet ministers including Alan Milburn, the Health Secretary, and Baroness Jay, the women's minister, have privately expressed their concern that the deal will undermine the Government's wider campaign against teenage pregnancy. They have warned that it could leave the Government open to accusations of hypocrisy similar to the "back to basics" campaign which dogged John Major.

Mr Blunkett has sought to head off the Cabinet revolt by making a reduction in teenage pregnancy a key aim for schools. Britain has the highest rate in Western Europe and 90,000 teenage girls conceive every year. 

Baroness Young, the Tory former leader of the Lords who has led the campaign to keep Section 28, said last night: "It is all very well banning 'inappropriate' teaching, but what does 'inappropriate' mean? Some people's inappropriate teaching would not be the same as others'." She said that unless a replacement was as strong as Section 28, meaning that it would ban the promotion of homosexuality in schools, then she would insist on the original section staying.

Lady Young said she was unlikely to vote against the proposals, "because I would find it rather silly voting against marriage". But that would not stop her voting to keep Section 28 when the Local Government Bill returned to the Lords. Stonewall, the homosexual rights group, welcomed the plans. Angela Mason, executive director, said the Government had done a good job in bringing together "different but sincerely held views".