Letter from Calcutta: Crammed into a darkened room not much bigger than a cupboard, a dozen children aged between three and six are sitting cross-legged on the painted cement floor reciting the Hindi alphabet.
Their calm and concentration belie the growing clamour in the narrow lanes outside, as tens of thousands of prostitutes, including the parents of these tiny students, emerge for an evening's trade.
Teacher Rita Bannerjee leads the recitation with the seriousness of a beadle as few know better just how vital these simple lessons will be in helping the children escape the fate that brought their mothers to the mean streets of Sonagachi, Calcutta's main red-light district and one of the biggest in the world.
Less than a decade ago, Ms Bannerjee was sitting in a room like this, learning tailoring skills which she says meant she did not have to follow her mother into Sonagachi's sordid calling.
Her mother, she said, was forced by economic circumstance into the sex trade, and the last thing she wanted for her daughter was a life of the same, so she sent her to learn a trade that would help her become financially independent.
"Before I learned to become a teacher, I was sewing, making tablecloths, handkerchiefs, saris and Punjabi clothing, embroidery, knitting," she said during a break in class.
"So I'm highly skilled and can look after myself now."
As the searing heat of the Calcutta day gives way to a clammy evening, women are beginning to pour into the narrow lanes where an estimated 27,000 sex workers ply an area covering just five square kilometres.
Even before nightfall, the place is packed with a potpourri of women of all ages wearing all manner of dress, from traditional saris to tight mini-skirts and platform sandals, lined up by the curb, lolling in doorways, striding up and down, calling out and gesturing to potential customers. By 2am it's impossible to move.
"They can be very aggressive, because there is so much competition," said Asim Mukherjee, who after more than 20 years of working with the prostitutes and their children is a familiar face in Sonagachi, and so avoids being groped.
As secretary of the Indian charity Janasiksha Prochar Kendra (JPK), Mr Mukherjee oversees programmes like that employing Ms Bannerjee, aimed at getting the children of Sonagachi's sex workers into mainstream schools or, if they are older, training them in a vocation so they can avoid being sucked into the trade themselves.
JPK's programmes are supported by Goal, the Dublin-based charity that has been in Calcutta for almost 30 years, funding and supporting local non-governmental organisations working at the grassroots of Indian society.
Like many here, Mr Mukherjee appears sceptical about the way in which the area and its inhabitants were portrayed in the film Born Into Brothels, which last month won an Academy Award as best documentary. It has been criticised for concentrating on a handful of children and avoiding examination of the lives of the many thousands of people living in and off Sonagachi.
The most severe criticism has come from Durbar Mahila Samannyay Samity, an umbrella organisation of about 60,000 West Bengal sex workers, whose secretary, Mrinal Kanti Dutta, is the son of a former prostitute.
He told Indian media the film did not accurately portray the lives and working conditions of Calcutta's prostitutes and was wrong in its claim that their children had to have Aids tests before being permitted to go to school.
"The documentary shows that mothers are just too keen to introduce their daughters into the trade. This is gross and it wrongly portrays our women," he said.
Contrary to the impression that little was being done for the children of Sonagachi's working women, Mr Mukherjee said: "There are many, many charities working in this area. Unlike what many people think, the sex workers have the money to care for their children, and the last thing they want is for their own children to end up in the sex trade. So many parents will jump at the opportunities we are offering."
Most of Ms Bannerjee's class will transfer to local government schools this month and, thanks to her coaching, most are expected to stay the course.
But those living with parents who can afford the small fee for JPK classes are the lucky ones.
Mr Mukherjee estimates that up to 25 per cent of Calcutta's prostitutes are aged under 14, and many end up here after being trafficked from rural India or across the borders from Bangladesh and Nepal.
While there is little premium on virginity or youth in the Indian sex trade, he said, children have longer working lives and greater earning potential.
Few studies exist of human trafficking in India, though Sumanta Chakraborty, a researcher with Children In Need India, said "the situation is getting worse" as rural poverty on the sub-continent rises.
Even when children were rescued from brothels, sending them home was rarely an option because "their social acceptance is low, their situation is wretched and they come back to the cities".
With little government awareness or care for child sex workers, JPK encouraged sex workers themselves to police their communities, Mr Mukherjee said.
"It will take a long time because this is a very big problem in India, but we feel like we are having an effect."