On a narrow, rubbish-strewn street in south Beijing, one spotless building stands out, a former grain shop with whitewashed walls and potted plants by the door, which on close inspection turns out to be a school.
Inside there is a play room with a few climbing frames, three small classrooms for about 30 children aged two to seven, all with concrete floors, and a tiny office with a map of China and tables showing times of classes in reading, writing, singing and dancing, mathematics, art and English.
With its happy atmosphere, it could be a model of official Chinese primary education, but the remarkable thing about this little school, which I came across in a shanty town of sweat shops, street cafes and vegetable markets known as "Zhejiang Village", is that it is completely outside the state school system, and relies totally on parents paying monthly fees for its existence.
In the office over glasses of hot water, the headmaster said proudly he established the school last month with a small staff of training-college graduates. "The parents bring the children at 6.30 and they stay here until 5 p.m."
The master (who asked that his name not be used) said he and the children are all from the poor southern province of Zhejiang. They form part of a vast population of 2.6 million "undocumented" residents living illegally around the Chinese capital.
Normally the only migrants who come to the attention of foreign visitors to Beijing are beggars and flower-children. But they are the life blood of the city. They are the tailors, the hairdressers, the milk delivery boys, the street cleaners, the construction workers building the new office towers and metro line, the pedicart drivers who haul away "night soil" (human waste), and also the black marketeers and prostitutes.
They control the huge garbage industry which has its own hierarchy, with scavengers at the bottom and tip bosses with mobile phones at the top. Most of the "Zhejiang village" migrants are garment workers who provide Beijing with much of its clothing (some made from fibre produced by recycling plastic collected in the city dumps), which is often sold on street markets with genuine-looking designer labels.
Making clothes and moving rubbish are among the few jobs migrants are able to do in the Chinese capital, where unemployment is a growing problem among the local population of over 12 million. To protect the jobs of Beijing workers, the city has just increased from five to eight the number of industries from which migrant workers are banned, and from 34 to 103 the prohibited categories of work, such as tourist guide or waiter.
Worse still for the "undocumented", many more of whom are pouring into the city each day seeking a better life, the Beijing Public Security Bureau started a month-long drive on March 1st aimed at evicting one million migrants. On the streets police randomly stop outsiders, whom they can distinguish from locals by their slightly different ethnic features and the fact that they don't have that certain superior Beijinger attitude, to check their documents.
They look for the "Three Nos" - no temporary residence permit, no identification card and no employment permit. Anyone caught is taken to a detention centre and made to perform hard labour to earn a one-way ticket home, and then put on a longdistance train. The other day I saw several pedicarts doing Uturns, and people melting into alleyways, when policemen began checking documents in "Zhejiang Village".
A climate of fear and uncertainty is nothing new for those who live on the edge in Beijing. Four years ago the authorities broke up the garment district using armed police and soldiers. Last year 300,000 migrants were expelled to "tidy up" the capital for the country's 50th anniversary, including hundreds of ethnic Uiygar residents of "Xinjiang Village" north of the city, whose makeshift shish kebab cafes - popular with foreign students - and minarets were bulldozed away. But often they find their way back within weeks.
Beijingers do not like the migrants, and blame them for unemployment and crime, but they cannot manage without them. During the Chinese New Year in February, when people all over China returned to their home villages, stories appeared in the Beijing newspapers about milk deliveries not arriving and about how hard it was to get home help during the holiday week.
The little school in "Zhejiang Village" is only one of hundreds in Beijing where local communities have to run their own unofficial education programmes to try to give their children a better chance in life in a two-tier society. They operate openly but the children's parents can fall foul of the crackdown at any time.
"The government doesn't give any support to people like me," the headmaster said. "But if there is no such school as we provide, then the children will just be throwing stones at each other in the streets, or going begging."