Mr Cameron likens his efforts to missionary work - without the travel he so fears. "I don't like flying. I'm just frightened of all the possible risks of visiting other countries. But I can do something from here."

Mr Cameron's farm near Tooraweenah - population 76, about 60 kilometres from Coonabarabran - was seen as an ideal testing ground because the conditions were similar to those in some Third World countries. Among the teething problems he identified in early XO versions was a battery that failed to charge when the temperature reached 45 degrees. He has also helped develop the free software used on the XOs. But his greatest contribution has been testing the range of the wireless connection between laptops on the long dirt roads and across the hills of Warrumbungle National Park, near his home. The XOs use a wireless mesh network that connects all laptops within range - without the need for infrastructure such as routers or cables - so children can collaborate on any computer activity.

The charity's vice-president of software engineering, Jim Gettys, was in Australia this month to give an update on the project to a conference of free-software developers. In recent weeks the first batch of 250,000 XOs has been sent to Peru, and charity staff have visited Mongolia to show teachers and students how to use the computers.

Mr Gettys described some of the hurdles they had had to overcome - children's homes without electricity, low literacy rates, no knowledge of the internet in some communities and languages in which computer terminology has yet to be created. The laptops have a hand-crank or a solar panel to power them, a screen that can be read in bright sunlight, sturdy handles and dust-resistant keyboards sized for children's fingers, and all the features of normal laptops - a camera and microphone, USB ports and game pad keys. "Children all over the world are just as able to learn as our kids," Mr Gettys said.

"They may have no place to learn except under a tree. Conventional laptops are pretty useless in that instance."