When Joana arrived in England three years ago, the mere thought of going to school made her physically sick. Her mother remembers it well. “In the first weeks, the nerves she had, just thinking she had to go to school - she would end up vomiting. I used to go to work very worried.”

The problem in those early days was largely one of language. Joana’s family had just moved to England from Portugal, and they spoke no English. Once she had cracked the language barrier - and, like most children, she was a quick learner - her nervousness evaporated, and before long she was enjoying life at her secondary school on the south coast.

But for children like Joana, 14, mastering English is only half the battle.

Educationists in the UK and Portugal have long recognised that children of Portuguese migrants in Britain underachieve dramatically.

In the London borough of Lambeth, where, over the past few years, the Portuguese have become the third largest immigrant group after Caribbeans and Africans, their performance at key stage 1 is the lowest of any ethnic group in the authority. Underachievement at key stage 2 and GCSE has also become a major concern.

Feyisa Demie, Lambeth’s head of education research and statistics, says information about new groups is scarce, as they are not recognised nationally as a separate category. “But we are talking about 6 per cent of the school population. In one of our schools, 85 per cent of the students are from the Portuguese community.”

Ms Demie has no doubts that Portuguese students are underperforming in Lambeth. “We have been focusing on Caribbean children, but we are trying to set up a conference and bring the Portuguese into it. We want to see if it is possible to get EU funding to support people from Portugal. Negotiation is going on with the consulate.”

As long ago as 1976, Ana Santos, the first officer of the Portuguese education department in the UK, wrote: “As happens with a number of other minority groups, the school performance of most Portuguese children now settled in London appears to be below that of their British peers.”

But not until the end of the millennium was any attempt made to address the problem. By this time, Portuguese workers had begun taking full advantage of European Union membership, and were settling in countries such as France and the UK, where even the minimum wage can be considerably higher than earnings at home. But in Portugal the education establishment was concerned that an unexpected downside of this otherwise welcome freedom of movement was underachievement among the children of migrant families.

In 1999, the Portuguese government, supported by the Calouste Gulbenkian Foundation in London, commissioned Dr Guida de Abreu, a psychologist at the University of Luton, to direct a research project on the experiences of Portuguese students in Britain.

When she started work, Dr Abreu was astonished to discover that there was no existing research into the Portuguese community in Britain, in sharp contrast to the many studies on other migrant groups of similar size.

Reporting on her findings, she echoed the words of Feyisa Demie, referring to the “invisibility” of Portuguese students in British schools, who, as white European citizens, “apparently manage their lives without being counted in the formal statistics”.

Schools tended to put the students’ poor academic performance down to their lack of English. But as Dr Abreu and her team started interviewing secondary students and parents on the south coast and the Channel Islands, where many Portuguese families have found work in the hotel and catering industries in recent years, a more complex picture emerged.

These Portuguese communities were “well networked”, with many informal community translators enabling new arrivals to build relationships with employers, banks, schools, and housing and health services. But as soon as parents perceived their child had got to grips with the English language and local ways, the child had to take on the translating and negotiating role in place of an outsider. “In short,” says Dr Abreu, “the family needs require their children to develop bicultural identities.”

At this point, the researchers found an enormous gulf opening between the lives of Portuguese students and their English classmates. In a reversal of the usual situation, Portuguese children were routinely expected to take time off school to accompany their parents to medical and other appointments. As one Portuguese girl put it: “Their parents go with them, I go with my parents.”

“Thus,” wrote Dr Abreu, “these children live between two worlds, which are not free of conflict. One is the world of the school that expects them to behave as teenagers of particular age groups, whose main working responsibility is studying, and who show a certain degree of dependence on their parents. Another is the world of their homes that expects them to make a substantial contribution to sustaining their families’ lives, assuming adult roles that sometimes may take priority over schooling.”

When it came to parental involvement with the school, the researchers found that many Portuguese parents were put off by their lack of language skills.

All contact was therefore mediated through the child, leaving parents powerless to monitor or influence their children’s educational progress.

Meanwhile, Portuguese students who had become kingpins in the family setting found themselves isolated at school. If they spoke Portuguese to their friends or talked too much about Portugal, English students regarded them with suspicion, and many felt torn between fitting in and wanting to hold on to their identity.

“Interviews with their teachers revealed very little recognition of the process of cultural identity development,” Dr Abreu wrote, and she called for a more informed debate about schools’ role in shaping cultural identities. “The assumption that the desire of all the children is to fit in cannot be taken for granted.”

At Stockwell primary school in Lambeth, where 150 of the 450 children on the school roll have Portuguese as their first language, headteacher Janet Mulholland employs a teacher from Portugal, and seven assistants who speak Portuguese or Spanish. “Our receptionist also speaks those languages,” she says, “so there is always somebody around who can help out with pupils or parents.”

While most other ethnic minority groups in Lambeth have lived in the UK for two or three generations and are familiar with the English language and the local education system, the same cannot be said of most Portuguese families, says Ms Mulholland. Many come from the relatively poor island of Madeira or from more rural parts of the mainland, and may be illiterate in Portuguese, having received little or no schooling in their own country.

To help address these problems, Stockwell runs after-school classes for all key stage 1 children wishing to learn Portuguese. The classes are funded by the education action zone, while the Portuguese embassy funds and runs daily Portuguese lessons for all local key stage 2 children.

The majority of Portuguese families coming to the UK work in hotels and catering in London or on the south coast. But others have been recruited in Portugal by British-based staff agencies to work in low-paid jobs in agriculture or the food-processing industry, and so find themselves living in rural areas relatively unused to immigration.

One such area is Norfolk, where a large Portuguese-speaking community has grown up in the space of two or three years. But far from regarding Portuguese children as a problem, Nancy Robinson, headteacher at Charles Burrell high in Thetford, sees them as a boost to the school’s record on inclusion.

Portuguese parents are queuing to get their children into the school, and a key factor has been the hiring of a Portuguese learning support assistant.

Ana Marques, whose daughter is a student at Charles Burrell, was a youth worker in Portugal before coming to England, and her brief is to support all students, whatever their nationality.

“If I had more resources, I would like to appoint someone else like Ana,” says Ms Robinson. “The best way of using a Portuguese member of staff is not just for the Portuguese. Promoting multiculturalism within the school is then a positive offshoot.”

While her brief is to support all students, Ms Marques has special responsibility for liaising with Portuguese parents. Nico Dobben, an assistant head who oversees the school’s inclusion policy, says: “They are supportive and interested, and the Portuguese kids who have been here two years are, on the whole, working hard. They have the normal range of ability you would find anywhere, and a couple of the kids are outstanding.”

As well as Ms Marques, the school employs a language support assistant one day a week to help Portuguese students develop their English.

And so they can maintain and develop their own cultural identities, the school plans to offer Portuguese at GCSE for anyone who wants to take it , and to set aside a day for celebrating Portuguese culture.

“The school’s ethos is to see such issues as a challenge rather than a problem - an opportunity rather than a threat,” says Ms Robinson.