Schools need to become more accountable for pupils who go missing without trace every year, children's groups warned this week.
Fears are growing that children vanishing from school rolls in Wales could be forced into prostitution, arranged marriages, domestic labour or begging.
Campaigners say teachers need to keep better records and be more vigilant of "at risk" pupils with high rates of absenteeism.
The warning comes as an Assembly committee investigating the trafficking of women and children in Wales meets for the first time.
Chair Joyce Watson, Labour AM for Mid and West Wales, said schools had a duty to monitor pupils more closely. "The extent of child trafficking in Wales is unknown," she said. "But some children end up in care for 48 or 72 hours before disappearing.
"We need a system for monitoring children missing from school."
The group's work will help bring Wales into line with the Council of Europe's Convention of Action against Trafficking of Human Beings which the Westminster government is set to ratify in December.
Jane Hutt, Wales's education minister, is to work with the committee. Cardiff has also become the first local authority in Wales to issue multi-agency protocols on child trafficking.
Issued through the Cardiff local safeguarding children board, they maintain that schools must have better monitoring systems.
Figures released by a Home Office select committee earlier this month revealed that at least 2,000 pupils were unaccounted for in England last year.
It was thought a large proportion of these were girls removed from education and forced into marriages overseas. The number of young British Asians coerced into marrying abroad could be as high as 3,000 a year - 10 times the official estimates.
The proportion of ethnic minority pupils in Wales has risen by around 20 per cent over the past three years, increasing fears for girls forced into arranged marriages.
Simon Jones, policy and public affairs manager for children's charity the NSPCC Cymru, said schools have a key role in identifying and safeguarding trafficked children who have been abused, and who often miss out on an education.
"Education professionals and non-teaching staff often see children more than any other agencies, and can spot when a young person is worried about a situation," he said. "We have to be aware that not all these young people will be in school."
David Evans, NUT Cymru secretary, said schools were already following the relevant protocols and that all agencies have a role to play.
"Teachers who see that children are not attending school, or are in danger of dropping out, already have a system for appropriate referrals," he said. "I can't see what additional measures could be put in place. "The matter is then out of the school's hands and with social services and the police."
According to a recent report by the Child Exploitation and Online Protection Centre (CEOP) on trafficking, most young victims are aged between 14 and 17.
But recent research by the children's rights organisation Epcat found UK authorities were overestimating the ages of children illegally brought into the country, leaving some minors without access to housing or schooling.
Mr Jones said co-operation between schools, social services, immigration authorities and other agencies is essential to help children who may have been trafficked.
However, the CEOP also found that more than half of the 330 children trafficked into the UK in 2005-6 vanished from care. Welfare groups believe the figures are gross underestimates.
The evidence for trafficking in Wales is mostly anecdotal, but research by Amnesty International found that the trade persists, both in cities and small communities.
The Assembly government has issued draft guidance for child agencies to recognise trafficked children. Signs include physical abuse, increased sexual behaviour or language, frequent absenteeism, not being enrolled with a GP, or girls being driven around by an older male or "boyfriend".
The Assembly government found evidence that traffickers register children at school for short periods before moving to other towns in Wales or outside the UK.
Trafficking often occurs near ports. Ireland is seen as a growing sea route for children brought into Wales illegally.
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