Foreign exchanges can take a surprising turn. One friend of mine found herself, at the age of 14, accompanying her French hosts to a nudist camp. That was an exchange arranged by her family. But even exchanges arranged with every care by schools can go wrong. You cannot guarantee that exchange partners will get on with each other or with each other’s parents or siblings. Nor can you stop teenagers being faddy about food overnight.

Yet any language teacher knows that nothing trumps living with a foreign family to make real progress in speaking a language and do a fair bit of growing up at the same time.

“You definitely notice their language skills improve,” says Helen Myers, president of the Association for Language Learning (ALL). “It boosts their confidence and really does give them more of a reason to continue. You can’t beat one or two weeks of just being surrounded by it on road signs and so on and living in a family and hearing the same things again and again.”

So it is worrying that the number of exchanges seems to be declining even faster than the numbers studying most foreign languages. Although figures are hard to come by, language teachers agree that the traditional exchange is in danger of dying out. Those that do still take place are generally long established, often the result of town twinning.

The reason for the decline is not money (most exchanges are quite cheap), but our risk-averse culture. The same health and safety concerns that have caused the virtual demise of lab experiments and geography field trips have almost done for exchanges. What, nervous parents and school governors ask themselves, could be riskier than letting a teenager stay with an unknown foreign family?

“When parents start asking about a criminal record check and schools can’t confidently give a satisfactory answer, the whole idea goes out the window,” says Duncan Byrne, assistant head (and former head of languages) at Haberdashers’ Aske’s Boys’ independent school in Hertfordshire. “You can’t submit families to criminal record checks in countries like France it’s just not part of their culture.”

It is this fear of abuse and worse that is behind the rise of the short, “sanitised” foreign trip, which has largely replaced the full-blown exchange, he says. “That’s not a language trip: it’s a cultural trip.”

At The Ashcombe School in Dorking, Surrey, exchanges at one time attracted too few pupils to make them viable. But when the school became a specialist language college in 1998, it decided to take action to stop the rot. It used some of the specialist funds to pay for a member of staff who would organise a graduated programme of foreign trips and exchanges.

Today, pupils are broken in gently to the idea of going abroad. In Year 7, when everyone takes both French and German, nearly all of the 240 pupils in the year go on a five-day trip to the Rhineland. In Year 8 comes the opportunity of a trip to an activity centre in Normandy, taken up by well over half the year group. On this trip, they have to use French every day, for instance to buy food for their picnics.

So when, in Years 9, 10 and 11, pupils finally get the chance of an exchange, they are intrigued rather than horrified by the prospect. Take-up is high: 55 for France and more than 20 for Germany last year, with others going to Spain and Italy.

“You must know how to manage exchanges,” stresses Helen Myers, deputy head of Ashcombe as well as being ALL president. “Not every pupil will be happy and you must make it clear you will help not just abandon them for two weeks, as schools used to do.”

Two teachers, with adult helpers and parents, travelled to France with the party of 55 to keep tabs.

Exchanges are well worth the effort, she adds. “It’s a unique opportunity. And for some it leads to a lifelong friendship.”