Once you get inside, it could be any information technology classroom. There are rows of screens and office chairs, a carpeted floor, fluorescent lighting. This, however, is a roving Computer Gym, a fully-equipped mobile classroom on the back of a white flatbed lorry.
It's one of a small fleet which have been doing the rounds of after-school clubs, nursery schools and community schemes in London and the south-east, bringing technology to children and adults who might otherwise miss out.
On a housing estate in Dulwich, south London, people wander in to use the PCs. Tutor Chris Colnaghi supervises one lad who is exploring South America using an interactive geography game. Opposite him a girl plays a lateral thinking game with on-screen creatures called Fripples.
Amanda Cox, director of Computer Gym UK, says there are often queues at the door: "On one estate in Ilford we regularly get 60 children a day. There isn't enough for them to do there. They're not getting enough IT at school, and parents are happy they're doing something constructive. But most importantly, they're having fun."
Computer Gym is a family business, started in 1992 in Australia by Cox's parents, British expats Carl and Louise Planting. Now there are 19 franchise operations run nationwide in Australia; in Queens-land the company has become the main provider of IT to primary schools.
Three years ago Cox brought Computer Gym to Britain. The company is based in Thames Ditton, Surrey, and employs three full-time and seven part-time staff, five of them qualified teachers.
It offers courses structured over 12 weeks, keeping records so children can pick up where they leave off. "We have eight computers, and software for children aged from two to 12," says Cox. "There's maths, science, English, geography and history - we try and weave them into each term so that children do a little bit of each one. Older children would be doing things like writing stories, or database work."
With the help of outside sponsors, Computer Gym also delivers family literacy and numeracy projects, courses for disaffected teenagers and adult education programmes aimed at helping with a CV, job application or the basics of computers.
This community role has caught the attention of the Government's Social Exclusion Unit. Its report, Bringing Britain Together?, highlighted Computer Gym's work with the London-based housing association, the Peabody Trust.
Out of a sample of 30 adults Computer Gym helped with training and career counselling sessions, 10 were referred to colleges for further vocational training, while five went on to get jobs. And feedback from local schools shows it has a "positive impact on the classroom performance of many of the young people involved".
It all costs, of course- about pound;5 per child for a half-hour session and about pound;500 a day for an average-sized school. Most of Computer Gym's work is with nurseries or after-school clubs - where parents pay for the tuition - or in private schools or community projects with sponsors.
Berrymede Junior School, on a deprived high-rise estate in Acton, is one of the few state schools to benefit from Computer Gym, purely because it is sponsored by West London Training and Enterprise Council. Headteacher Beverley Randall says: "We have one computer in each class, but the children have very little chance to get on it. With Computer Gym they get their own machine and they move forward much more quickly. It's like having our own IT centre."
Randall is now aiming to have her staff trained in the mobile classroom. "Computers are all right while they're working. But when they go wrong, who is going to fix them? There are so many hassles. Although we are all willing, and want to get IT going well, there are so many things that go against you all the time. When Computer Gym arrives, the machines are up and running."
So will such mobile IT classrooms become a common sight in schools? Cox says only if they become official information technology providers, as in parts of Australia. "Ultimately we do need to become involved during the school day. The extra-curricular model is fine, and that will keep going, but I think our ultimate goal is to become involved with many more state schools.
"There are problems with IT that I don't think will ever go away - maintenance, hardware and software, procuring it, getting somebody trained up to look after all that. It's just the hassle factor.
"Schools spend so much money on buying equipment which quickly becomes outdated, and they're stuck with it. Then the new software comes out and they can't run it because their equipment is no longer compatible.
"Rather than having to spend on things which are going to become redundant, they could be spending it on a service which they don't have to worry about. It's all taken away from them, so that teachers can concentrate on all the other things they do so well."
Computer Gym: 0181 224 6444