By Liz Stephens
The government's Forced Marriage Unit (FMU) received almost 800 calls for help in the first six months of this year, some allegedly from children under 16 years old.
With school holidays looming, new guidance has been published urging schools to identify those at risk of forced marriage.
Experts say there is evidence that abusive families use the school summer holidays to coerce daughters and sons to marry abroad.
The guidance came as an official report highlighted that some schools have failed to act on suspicions or evidence of abuse.
Critics say a few schools have been reluctant to intervene as they view forced marriage as a "cultural issue" or fear a backlash from powerful figures in minority communities.
The report calls on schools to play a greater preventative role.
Foreign Office minister Chris Bryant told BBC Radio 4's Today programme: "I should make it absolutely clear there is no culture and there is no religion in which forced marriage should be acceptable or indeed is acceptable."
He urged professionals to "keep their eyes wide open".
"There are key times of the year, particularly if an elder sibling has married very young or suddenly left school, if a youngster is self-harming or if they are constantly being accompanied by parents, even to a doctor's surgery," he said.
Jasvinder Sanghera of Karma Nirvana, a national campaign group against forced marriages, urged teachers to act on suspicions.
"This is not something you must be culturally sensitive about," she said.
"This is a child abuse issue, and you must treat it in that way and follow your child protection procedures. Do not turn a blind eye".
There are estimated to be at least 5,000 cases of forced marriage every year, but figures are difficult to pinpoint as most incidences go unreported.
UK courts have made 36 forced marriage prevention orders - a recently created power to stop UK citizens being taken abroad against their will.