But gappers are not the only "colonialists". There is another group of well-meaning visitors who should know better: the linkersJ- heads and teachers who travel abroad with generous government funding to link up with schools in poor countries that often cannot afford the return visits.
Links with developing countries have grown fast in the wake of Make Poverty History and Live8 last year. On the face of it, links increase our knowledge about the outside world and enrich the curriculum. Many teachers say their trips to partner schools in poor countries are not just eye-opening but life-changing experiences. Their enthusiasm is palpable.
Yet there is a suppressed guilt over the problem that many dare not speak aloud. For every excellent link that benefits both sides, there may be four or five that do no such thing. The losers are invariably the poorer countries.
Daleep Mukarji, head of the charity Christian Aid, is one of the very few people to admit openly that linking benefits rich countries first.
"Only after a considerable time, when a common sense of purpose has developed between two schools, does it begin to benefit people in the poorer country," he said at a UK One World Linking Association conference.
Most ideas and projects - and even the way of working together - come from the richer partner whose government funds overseas travel. "We may be guilty of trying to make our partners more like us - in effect a kind of cultural imperialism," says Dr Mukarji.
Focus on fulfilling the curriculum can mean the needs of partner schools are ignored or sidelined. Our history and geography teachers proudly stock their classrooms with genuine artefacts, much as the British Museum was stocked with trophies during the colonial era. Schools in poorer countries have openly commented on feeling "used" as sources of information or as a resource for UK schools.
In the worst cases, they become dumping grounds for old textbooks, shabby toys and outdated equipment. Pre-pentium computers gather dust in African schools. Colour pencils are sent to India, where cheap pencils are readily available - it costs more to send them than to buy them locally. Cast-offs are demeaning and often useless.
People in poor countries are friendly and welcoming but they wonder what rich countries want from them. They do not always see linking as beneficial in their day-to-day struggle for survival. Many links start with fundraising by the UK school. The partner school begins to expect "gifts", and in the worst cases become dependants rather than partners. Many teachers seeking help from the British Council on linking problems want to break out of the fundraising, aid-giving relationship and re-establish the link on a more equal, educational footing.
"You have to face the unequal world before you can talk of one world," says Sharon Leftridge, links co-ordinator of Polesworth school, in Tamworth, Warwickshire. Like it or not, money is a major issue. Dr Mukarji says the problems of inequality are underestimated by teachers and that "we are simply in different worlds in terms of power and history".
Linking requires painstaking groundwork. It is no coincidence that the best linkers understand poverty and development and become campaigners for change, fairer trade and debt relief. But the obstacles are no reason to dump links. Remote village schools in poor countries feel part of the wider world through linking. It excites pupils and brings lessons alive. It is as uplifting for their teachers as for ours.
Even if schools are unequal in resources, they can be equal in sharing experiences. Our teachers return from Uganda with fresh ideas about family literacy. They visit Brazil and learn new approaches with deprived, inner-city children.
Young people want to make the world a fairer place. Dr Mukarji says:
"International relations are too important to be left only to governments, diplomats, UN agencies and international institutions. They have not been very successful. We need people-to-people contacts, friendship, personal relationships and many ways of linking so that we can make this a better world for all."