One parent could do as well as two, Jackie Anderson, the association’s president, told its annual conference in Glasgow. A loving, stable relationship with one person could be enough to nurture a well-balanced individual.

Mrs Anderson, who has been married for 35 years and has a son and daughter - both grown up, said the recent Green Paper on the family was quite right to emphasise the desirability of the traditional family. But in reality it was not always possible. Elizabeth I and Cherie Blair were examples of successful women brought up in unconventional families.

Mrs Anderson, head of King’s high school, Warwick, said her own pupils all expected to marry and were very realistic about the difficulties of choosing between a career or children or combining the two.

Later, she said the emphasis on the traditional family might make girls of divorced families feel worse. As for single mothers who were trying to do a job and look after their children: “they already feel a failure because their marriage has broken up and I see no point in harping on that.”

Last month Patrick Tobin chairman of the Headmasters and Headmistresses Conference which includes the leading boys’ and mixed public schools, told his annual gathering that marital break-up was the biggest single cause of disciplinary problems in schools.

But girls’ schools heads said this week that girls reacted differently to family break-up. They might become sad or lose their self-esteem but they tended to talk to other girls and teachers. Boys tended to bottle things up and might then lash out and “go off the rails spectacularly”.