``Go on then, what's 300 million multiplied by 400 million? Tell the teacher,'' Zhang challenges her.

Before his chum can even begin the task, Zhang taunts: ``See you don't know. You can't be a teacher; you're going to be a farmer.''

Zhao gets her revenge when I ask Zhang if he knows the name of the president of the United States. Zhang thinks for a while, his scuffed tennis shoes swinging back and forth, his fingers twisting into shapes on his school uniform tracksuit bottoms.

He admits he doesn't know, but he quickly adds: ``I know the president of China - it's Hu Jintao.''

It's a scene familiar in any school anywhere, except that both these children are deaf and are communicating entirely in Chinese sign language.

What makes this unique is that for the past 50 years, sign language has been actively discouraged, and in some cases banned, from classrooms in China. Despite evidence showing that deaf children are visual learners, and that those who learn sign language perform better in school, educators have insisted they learn to speak so they can blend in with their hearing classmates at public school.

Since the 1980s, nearly 1,500 pre-school ``hearing rehabilitation'' centers, run by the quasi-governmental China Disabled People's Federation (CDPF), have fuelled many a parent's dream that hours spent mimicking words will eventually unlock their child's linguistic talent, and release the family from the shadow of disability.

Yet, according to statistics compiled by the CDPF, fewer than 10 percent of China's 800,000 deaf preschoolers will reach the age of compulsory education - seven years old - with an adequate grasp of the spoken language to join a public school.

Those who do benefit from the oral-only approach, and there are some success stories, are usually children with residual hearing, or who lost their hearing after they learned how to speak, or who can afford cochlear operations and special language training.

``It's so difficult for the children to learn to speak,'' says Hu Aixin, who has been teaching deaf children at Tianjin Number One School for the Deaf for the past 20 years.

``They need 45 minutes just to learn one syllable. For vowel sounds, it is easier - they can see the shape of the mouth. But for the sounds they can't see - each shape can have different meanings depending on the tone. It takes a lot of time.''

Hu says that up to 70 percent of lesson time is spent teaching children how to say basic words such as mother and father. Math, science, literature and even playtime all take a back seat to oral drills. It means, she says, that children are missing out, not only on a quality education, but also on crucial life and communication skills.

As a result, most deaf children are expected to leave school with an education level at least three grades below their hearing peers, and with few job prospects beyond factory work.

``It's not that deaf children aren't as smart as the hearing students, they've just never been given a chance,'' Hu says.

That this oral-only policy has contributed to the creation of a poorly educated and marginalized community of some 22 million people seems to have escaped the attention of the government - until now.

Over the past few years, local authorities in Tianjin City, and Jiangsu, Yunnan and Anhui provinces, in cooperation with groups such as UNICEF, Save the Children UK and the Amity Foundation, have been charting a new course for deaf education.

Using what is called in the West the bilingual and bicultural - or bi-bi - method, children gain a language they can communicate fluently in while also being given lessons in deaf culture and an identity they can be proud of.

Four years ago, Tianjin Number One School for the Deaf eschewed the oral-only method and adopted sign language as the main method of communication, employing deaf teachers to teach the language and culture of the deaf - both radical departures from the norm.

At first, the new approach was limited to just two preschool classes, but in September 2004, Zhao and Zhang joined a handful of deaf children in the country's first bi-bi primary school class.

``The difference is that the emphasis is on recognizing and understanding the word, not on its pronunciation. So it's a lot more effective and takes a lot less time to teach,'' Hu says. ``You can really see them communicating with one another.''

Six-year-old Zhao provides her own assessment of the new bi-bi program: ``Oral isn't very clear, sometimes I don't understand. But with sign language it's easy for me to understand.''

A few blocks away, five-year-old Li Hao lets out a shriek of delight when he sees me, and streaks across the classroom floor. One hand reaches out to grab mine and pumps it furiously, while the other is a flurry of movement as he signs ``Hello auntie'' and then ``camera'' and some other words I cannot catch. Within minutes, I am thigh-deep in tiny preschoolers who all want to shake my hand and sign, ``Hello.''

Li's teacher finally coaxes her charges back to their seats and Li flashes me a cheeky grin before reluctantly turning his attention to the pronunciation of Chinese vowel sounds. Across the room, four or five other children are telling stories in sign language, while a third group examines and questions their deaf teacher, Wang Jian, about an egg he is holding.

When I first met Li a year ago, he had only just joined the bi-bi class. Like more than 90 percent of deaf children, both Li's parents can hear and were at a loss as how to communicate with him.

Unable to sign or speak he became frustrated at his inability to make any one understand him, says his mother. Today, however, he is a star pupil, an avid sign storyteller and full of uninhibited curiosity.

``The biggest change in the children is in their personality,'' says Li Qinyuan, one of two hearing teachers in the preschool class. ``Many came to us shy and insolent. They couldn't communicate or make anyone understand them and it showed in tantrums and in frustration. But now it's like sign language has opened a door in them and allowed them to be themselves.''

It is not just their personalities that have changed, but their academic achievements too.

``These kids know more at four or five than I did at eight or nine,'' says Wang Jian, through a sign interpreter.

News of the experimental class is spreading. Deaf schools across the country are asking for more information and training in the approach. Local TV and media have run stories about the children, and in January the Hong Kong education ministry paid a working visit.

Yet, with such tangible and notable results, why is it that only a handful - just 33 children - have enrolled in the bi-bi class at Tianjin Number One School for the Deaf in the past four years?

Parents are the program's biggest resource, say school officials, but also its biggest obstacle.

``Parents' attitudes are hard to change,'' says Professor Zhao Mingzhi, an ear, nose and throat doctor and director of the Tianjin Rehabilitation Centre for Hearing Disability. ``Many still believe that sign language is a bad influence. Their only hope is that their child will be able to speak.''

For the profoundly deaf, he says, the oral-only approach ``is unfair.'' They may be able to utter a few basic words, but this is not true communication. ``It is just for the parents. They convince themselves that because their child can say a few lines of a Tsang Dynasty poem that they can communicate,'' he says.

Many parents spend tens of thousands of yuan on Chinese medicine, acupuncture, rehabilitation centers and hearing aids. The upshot is that when all options are exhausted and their child still can't hear or speak, they may finally turn to sign language; but at that stage, children are well past the optimum time for language development, professor Zhao says.

But parents have a real fear that without the adequate infrastructure - such as sign language interpreters at universities and in public buildings - learning sign language could drive their children further into isolation.

``I don't see that it helps them to communicate with the hearing world,'' one mother of a six-year-old deaf girl in Yangzhou says. ``We have 20 deaf workers in our factory and they all sit in a big circle and talk in sign language among themselves. I don't know what to say to them, they don't know what to say to me. And it's too tiring to write everything down.''

Tianjin is one of the country's more liberal cities when it comes to deaf rights. It has the country's first deaf university, the first club to promote the use and study of sign language and a government that is willing to pump resources into a modern high-tech deaf school. But even here, deaf is still more a medical condition rather than an identity, as it has become in many Western countries.

Wang Xiuling looks perplexed. The 33-year-old deaf teacher is trying to think of some famous deaf people in China. Her colleague, Wang Jian, who is also deaf, names the vice-president of the deaf association, and a research scholar. But what about deaf writers, poets, actors or musicians, I ask? ``Empty,'' signs Wang Xiuling. Then her face cracks a broad smile, she signs in fluid movements, she waggles a hand on top of her head. I'm entranced by this mime.

Through the interpreter, I learn that there is a deaf dancer in a disabled dancing troupe who often performs the role of a swan.

``It's true that there is still a lack of awareness about what constitutes deaf culture, even among the deaf community,'' says Wang Liqun, one of the administrators at the Tianjin Rehabilitation Centre for Hearing Disability.

Part of the problem is that many in the deaf community are still struggling to come to terms with their identity, especially those in the 18-35 age group. ``They still haven't accepted they are deaf. They are still trying to integrate into mainstream society. Often they don't want to associate with the deaf community, or are forbidden to do so by their family.''

Which is why deaf teachers play such a pivotal role in providing children not just with opportunities to communicate, but with strong role models they can identify with.

They also show the children's parents that although their children are deaf, they can still succeed.

Wang Xingshun, 59, lost his hearing at the age of two, and because he attended a deaf school that only used sign language - before the introduction of the oral-only approach - he never learned to speak. It certainly hasn't stopped him from making his mark.

He arrives for our meeting on a motorized three-wheeler - the deaf aren't allowed to drive cars in China but motorcycles are a separate issue. Wang Xingshun brushes aside my concerns for his safety: ``It's true I cannot hear, but my sight and my other senses are a lot better than yours. They should call us sight-enhanced, not deaf.''

At 15, he was sent to work in a factory that made and exported steel components for cars. Although the Cultural Revolution put paid to any chance of further education, he gave it a second go at the age of 40 and enrolled at the Tianjin Technical College, studying for a degree in engineering. He achieved top marks and was promoted to the position of director of the technical department at his company. Being the only deaf person hasn't affected his work either: ``I taught my colleagues how to sign,'' he says.

But Wang Xingshun is an exception. Research carried out by Beijing Normal University found that most deaf college students had little respect for other deaf people, would prefer a hearing teacher over a deaf teacher and would rather try to assimilate into the hearing society than embrace a deaf identity.

``Most hearing people are not so familiar with sign language, so there are bound to be communication difficulties and misunderstandings,'' he says.

``It's like two of us, foreigners who speak different languages and who have a different history and culture. But as Chinese we must learn about Western history, we must learn your language in our schools, because your technology is more developed than ours.

``Who wants to learn about deaf culture, history and language? This is how we become a minority further isolated from society.

``If [hearing] people would just try to have a bit of sympathy towards deaf people - take the time to learn a bit of sign language or understand our culture - then it would be better for everyone.''