And when the cartoon-daubed vehicle arrives at the fly-infested camp, it is greeted by a mob of children who swarm around its door. For two hours, the team of social workers and teachers aboard use food and games to bring learning to some of the city's tens of thousands of children who have never been to school.
'We're developing a patience for school among kids who would never see the inside of a classroom-they live in the shadows,' said R M Mohla, coordinator of the slum education programme. The Chalta Firta, or mobile school, is Mohla's brainchild, an attempt to meet India's ambitious universal education target of getting all children aged between six to 14 into school by 2010.
But educators have met some resistance from slum dwellers, prostitutes and migrant labourers who say they prefer their children to work, in order to supplement meagre family incomes. The programme was inaugurated in January by the New Delhi government, which is paying non-profit groups Rs 3,000 per year per child to operate the four buses.
Parents were initially mistrustful of the mobile schools, worrying they may be a scam. After seeing it operate regularly for several months, their fears have been quelled, although convincing families to send income-earning children to school remains challenging. 'It's hard for us, we have no choice to make ends meet,' said rubbish-picker Kuppa, father of one of the scheme's success stories, eight-year-old Subyamarni, who is now in a government school.
Subyamarni spent his early childhood sifting trash and collecting recyclable plastic and other items with his father, but now spends evenings doing homework at home and working when he can. 'I like school because I can play games and learn to read,' said Subyamarni.
The bus drew Subyamarni in with its playful exterior-cartoons and pastel lettering make it look like a nursery school from the outside, although the television and stereo inside do give it the feel of a rock group's tour bus.
'In the beginning parents feared the kids would be taken away. They didn't know what was happening on the bus,' said social worker Durgesh Kumar Gupta, whose job is to knock on doors and convince families to send their children to the bus school.
Since its rocky beginnings, the pilot programme has enrolled half its 450 students in full-time government schools. The mobile teachers consult with the schools of enrolled children to monitor their progress. Parmot, a seventh grader living in the slum, helps the bus teachers by monitoring attendance of the scheme's graduates at the government school.
'I look for the kids at school and make sure they are coming. They need to learn,' the aspiring cricketer said. Students who had not showered in months now arrive at the bus with damp, freshly-combed hair and notebooks in which they have done their homework.
As the programme has expanded, the pair of teachers on board have found themselves teaching more than 70 children at a time