The Government expects teachers to play a key role in preventing girls as young as 13 from being taken abroad and forced into unwanted marriages.
Foreign Office guidelines are to be issued to schools next month highlighting the tell-tale signs to look out for in pupils who may be under threat.
Every year, hundreds of teenagers are taken overseas and married to men they have not met before. In many cases, the girls are forcibly abducted by their parents and raped by their husbands. Such marriages may also lead to enforced pregnancy or abortion.
The guidelines have been welcomed by Chris Keates, general secretary of the National Association of Schoolmasters Union of Women Teachers. She said:
"Teachers are trained to report changes in behaviour. They're interested in keeping children safe, whether in the context of forced marriages, abuse, neglect or health issues."
Warning signs for teachers to watch out for include a sudden loss of academic aspirations, self-harming and anxious or depressive behaviour, and a history of older siblings leaving education early. Teachers should also be aware that conflicts with parents over whether the pupil should continue in education may indicate that the parents have alternative plans for the child's future.
Several pupils at Mulberry girls, a comprehensive in east London which serves largely Muslim pupils, have approached their teachers for help in the past.
Headteacher Marlene Robottom said: "We try to support them through education. With an education they have more freedom of choice and they can become independent should they need to."
She said the Government's guidelines were most necessary in schools with only small numbers of Muslim pupils: "We've developed expertise, because this is part of day-to-day life. But schools where there aren't many minorities tend towards political correctness and may err on the side of caution. So the young person can end up quite vulnerable."
David Grahame, head of the forced marriage unit at the Foreign Office, said he hoped teachers would treat cases of suspected forced marriage as they would other personal problems. "Quite often, a young person won't think to approach the police, or they think it will bring shame on their family," he said. "Teachers need to create an atmosphere in schools where young people know their teachers will understand, and won't just laugh at them."
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EDUCATE THE PARENTS
Shuhena* was about to start her A-levels when her parents decided she should leave school and marry a stranger in Bangladesh.
The 16-year-old had hoped to finish school and possibly go on to university. But her parents flew her out to Bangladesh and forced her to go through an unwanted marriage ceremony.
She escaped soon after the marriage, with her older sister's help, and returned to England where she approached her school for help in contacting social services and receiving legal advice.
Her former head of year said: "The school can help to negotiate with parents, explaining the importance of education for females, and why their daughters should go to university.
"And we can refer the girls to agencies that offer advice and support.
"These girls are confident and articulate. There's a big sense of wanting to achieve and to get good jobs. But they have to educate their parents; let them know why exams are important."
*names have been changed
* Sudden drop in academic motivation or performance ("What's the point? I'll be married next year.");
* Truancy from lessons;
* Conflicts with parents over continued education;
* Excessive parental restrictions and control;
* History of domestic violence;
* Extended absence;
* Depressive behaviour;
* History of older siblings leaving education early and marrying early.