Within a few minutes of meeting Theresa Knott at the central London prep school where she teaches, it’s clear that, as she says, “first impressions can be so misleading”. I thought I was meeting a fearsome, early thirties, blue-stocking physics graduate with an interest in online learning.

The first surprise as we talk in the science lab, under the watchful gaze of a skeleton with fairy wings, is that this unassuming, fresh-faced teacher has two daughters, 15 and 18, and is a 40-year-old single parent.

The second is that she only obtained her degree five years ago, returning to college part-time to resume her studies 20 years after dropping out. The third is that, once her working day at Queen’s College Prep School is over, she has another life.

Theresa is one of a dedicated band of unpaid volunteers who act as the guardians of the Wikipedia online encyclopaedia - one of the great internet successes of the decade. The passion for sharing knowledge that is apparent in her teaching - she loves her Year 1s and 2s because, she says, they are full of wonder and enthusiasm for learning - translates after hours into tireless work for Wikipedia.

So firmly does she believe in its mission - to accumulate every piece of knowledge in the world in one easily accessible place - that she spends hours in the evening, or in the early morning before leaving for work, checking the site, editing pages and helping contributors.

She admits to choosing hotels with internet access when she goes on holiday so she can continue to check the site, although the recent purchase of a holiday home in Bulgaria without internet access has stymied that habit.

“I suppose I am a bit evangelical about it. I just think it’s such a great idea,” she says. Her zeal and technological expertise are particularly staggering for someone who, not so long ago, didn’t even own a computer. It was only while studying for her degree in 1997 that Theresa discovered usernet, the forerunner of the worldwide web, but she embraced the idea of a virtual exchange of information from the start.

“It was a struggle as a single parent with two kids to help through school; I needed resources. As soon as it was launched, I knew Wikipedia would become big and started contributing.”

Theresa continued even after she began her graduate teacher programme and then went on to Queen’s College. What she particularly loved about the early days was the feeling of community. “We all got to know each other well online. What is great about this sort of collaboration is that you get to know someone without any preconceptions. First impressions when you meet someone can be so misleading - you make a judgment based on appearance. On Wikipedia, you judge them purely on their knowledge and personality.”

So it is often a bit of a shock, she admits, to meet online friends in the flesh at Wikipedia get-togethers. “There was one guy in particular, who sounded so mature online, I was sure he would be a middle-aged professor, but when I met him he was about 20,” she laughs.

With only seven paid administrative employees, the encyclopaedia depends on the collaboration of its four million registered users, as well as countless others who edit the site anonymously. It is one of the most visited sites on the internet and is used as a reference tool for everyone from pupils to politicians. In 2003, Theresa was elected to the unpaid post of administrator by fellow Wikipedians, joining around 1,000 other veterans who act as moderators and guardians of the site.

A constant problem is posed by vandals who get their kicks by sabotaging high-profile websites. Articles on George Bush and abortion are obvious choices, but one cannot underestimate the childishness of bored internet vandals - the dyslexia article is a top target for anonymous users who enjoy scrambling the text. Theresa’s job is to visit a certain number of pages each day to check they haven’t been interfered with.

If she spots something, she can “revert” it back to its original state. She also has the power to block a vulnerable article from further editing, warn problem users about their behaviour online and temporarily suspend them.

Autobiography is discouraged because, Theresa says, authors may forget to keep a close check on their site and then are horrified to find libellous and hurtful edits have been inserted. Anyway, she says, Wikipedia is not a vanity site.

She is excited by new projects that she has been working on to bring greater resources online - particularly the “Open Clipart” project, which aims to provide useful diagrams and art work on the same basis as the written information on Wikipedia. “Someone will put a piece of work on the site, then people vote on whether it should join the clipart library,” she says. “Often I create a worksheet or diagram for my own teaching because I haven’t been able to find it elsewhere, so I eventually thought ‘why not share that?’” She is disappointed that she knows of no other teachers who contribute regularly to Wikipedia. “Some academics do, but their content tends to be very highbrow. The only people I’ve ever managed to persuade are the lab assistants,” she says.

Theresa’s online persona is steely, and, as an administrator reprimanding users publicly, she often ruffles feathers. She says she has become inured to insults and death threats. A recent classic ran: “So ur the worthless piece of shit that was deleting my edits on the Smallville page... I’ll track u down to where u live, u have no idea what trouble ur in. I’m gonna slice ur throat stab ur eyes out... ur a dead person.” She reported this user to his internet service provider and calmly carried on working.

But she enjoys an online joke too. Her personal page on Wikipedia carries this paragraph: “During Euro 2004, I painted the England flag on my tits in support of my country. Warning: if you are the sort of person who is easily offended by naked tits, do not click on the following link.” Do so, and up comes a skilfully edited photo of two fluffy avians with crosses of St George superimposed on them. The joke’s all the better for being completely unexpected. Once again, Theresa confounds expectations

Work the web

The name Wikipedia is a composite of the Hawaiian word Wiki, meaning quick, and encyclopaedia. It sums up the philosophy of the site’s co-founder, Jimmy Wales, who describes Wikipedia as “an effort to create and distribute a multi-lingual free encyclopaedia of the highest quality to every single person on the planet in their own language.”

Theresa says Wikipedia can be used by teachers in many different ways.

The most obvious is as an online source of information. The pros are that information can be found on almost any topic, and the number of contributors is such that it is likely to be full and well-balanced.

Information on the site is usually quickly updated if new discoveries are made. The cons are errors or false information.

Theresa says: “It is a good resource, but I would only use it with children old enough to understand that it is an open site and anyone can edit it.

“Children should not be allowed to edit content until they are old enough to know how to protect themselves and their identity from other users. We have had cases of children leaving their phone numbers on pages.”

Topics which are now “dead”, that is, established scientific principles or ancient history, are the best sites.

Paradoxically for older children, the knowledge that content can be manipulated or may simply be wrong, may be a valuable starting point for a look at objectivity in written reports and the importance of checking and cross-checking.

Theresa recommends teaching colleagues to take freely from the huge image library on the “Wikipedia commons” site. She also recommends the science diagrams, many of which she has found useful.

An advantage of the Wikipedia picture library is that it is all copyright-free, which means that you can use as much of it as you like - and, unlike Google, it is possible to print up pictures at full size.