London likes New Zealand teachers - and, as most young New Zealanders like to travel, it seems the ideal solution for schools desperate for staff. These young travellers sign up with agencies and go supply teaching, many of them ending up in schools that are difficult to staff. On returning home, they talk enthusiastically about their experiences, but they also bring with them disturbing messages about British schools.

They like the diversity and the variety. They enjoy contact with students from a mixture of cultural and ethnic backgrounds, especially if they have already travelled to some of the countries these students come from. They also enjoy trying out an assortment of schools from many parts of London. They grow in confidence when forced to deal with classroom situations likely to be more challenging than any they would face in New Zealand. And London is a great launching pad from which to see the rest of the world.

New Zealand teachers go overseas to gain experience, earn good money and travel the world. But some of those coming back talk with sadness about some of the schools they spend time in, and with frustration about their inability to make a difference. They say they have been given no chance to show what good teachers they are.

If you ask them to describe what they regard as a good day’s supply teaching, they say it is when you can get the students to sit down and be quiet, and there is just a faint possibility that you might teach them something that will be of use to them.

A “typical” day is one of surviving, with not too many interruptions, not too many students swearing at you, not too many mobile phones going off, not too many other classes being interrupted, and not too many students storming out of class.

A “bad” day is one during which someone - sometimes the teacher - gets hurt in class. New Zealand teachers ask how British teachers in such schools survive. They see that many are middle-aged or older, and they see the high turnover of young teachers. They note that British teachers are doing the best they can in difficult circumstances, and they admire the commitment of teachers who work themselves to exhaustion to give their students a chance in life. They find themselves in schools that provide stability for children within communities that are being ripped apart by crime and drugs.

They return with real sympathy for London children. It is a shock to arrive at a school that feels like a prison: locked doors, three-metre-high wire fences and almost completely covered in concrete.

New Zealand supply teachers must quickly come to terms with children who have been brought up in a true urban jungle. And they note the lack of outdoor activities. Ask any young New Zealander with experience of teaching in London what changes would make the city children happier and easier to teach, and you will be told to get a bit more sunshine into schools, get rid of some of the concrete and put in a couple of green playing fields.

London children lose their innocence much quicker than children here. The environment in which they grow up makes them more difficult to teach, but makes it more vital that they are well taught. Supply teachers from New Zealand do their best to meet that challenge, but all they can do is plug the gaps with the best intentions, with an eye on preserving their own personalities and sense of self-worth.

Britain needs our young teachers, and principals such as myself encourage those who go off on their “overseas experience”. We know they will return wiser, more experienced and with their classroom management skills tuned. We know they will be excited by London. But it can also become a stressful and grey place when you are not used to being surrounded by millions of people. That takes its toll when you are used to sun, the outdoors, sandy beaches, clean air, and a much more relaxed way of life. Nearly all young New Zealand teachers who go to London come home again. And, fortunately, most of them return home to teach.

Allan Peachey is principal of Rangitoto College, North Shore City, New Zealand