Bonjour, enfants: The English school that's serious about French

Haris has his hand in the air. He is stabbing at the ceiling and lifting himself out of his seat impatiently to tell the teacher what kiwis eat. "Vers, graines et balles. Ils cherchent leur nourriture en utilisant leur odorat," he declares triumphantly.

He's one of 28 children aged seven and eight in a bilingual class at a south London school that could become a model for the rest of the country. Since they entered Wix primary at the age of four the children have been taught all subjects in French for half the week and in English for the rest.

It's a trailblazing scheme backed by the French Embassy and the London borough of Wandsworth, a borough which says it has been so successful and popular with parents that it is introducing bilingual teaching at another of its primary schools.

Wix Primary School is in a narrow street off Clapham Common, and is unusual in sharing a site with the prep school for the independent, fee-charging Lycée Charles de Gaulle which follows the French curriculum. Until the arrival of Wix's headteacher Marc Wolstencroft six years ago, the schools were run separately and hardly talked to each other. Married to a French woman and with a bilingual daughter, Wolstencroft saw the scheme's potential and the two schools joined together to produce a bilingual stream made up of 14 children from the Lycée and 14 from Wix. Together the teachers worked out a new curriculum to satisfy the demands of both France and England.

Now in the first term of their fourth year of bilingual teaching, the Year Three class is doing comprehension with a challenging passage in French about the history and habitat of the New Zealand kiwi.

There are several noticeable differences between this class and the others in the "classic English" part of the school: the children, like in France, are not wearing uniform and they are sitting at desks facing the front instead of in groups around tables.

All the pupils get the chance to take part as Madame Catherine Souquière encourages them to read parts of the text and answer questions. So which children are French and which are English? It was impossible to tell. Haris, who I had put down as French turned out to be a native English speaker. "My whole family is English and Pakistani and Bengali," he says. "Some of my Mum's family has a bit of Chinese in them as well." I thought that a girl who had difficulty understanding that Kiwis were hunted in the 19th century for their feathers and are now a protected species was English – but in fact she was French.

Around half the English-speaking children have some link with France, such as a French-speaking parent. The rest are from families that want their children to be bilingual. "It's seen as the smart thing to do and people have moved large distances to be in our catchment area," says Wolstencroft.

Along the corridor, a group of five-year-olds in the reception year are learning to identify and name emotions from the exaggerated facial expressions of their teacher, Monsieur Pascal Marechau. They are clearly enraptured by his Gallic enthusiasm. In the English part of the school this would be carpet time, but the French prefer to seat them on low benches.

The bilingual stream is a brave experiment that involved a significant departure from the English national curriculum. It could have have gone badly wrong, admits Wolstencroft. Instead, it has been so successful that it has won praise from Ofsted and he believes it could be a model for other towns and cities and different languages.

Wandsworth is planning to introduce some bilingual classes at Hotham primary in Putney, though the core subjects, English, maths and science, will be taught in English, and it has introduced Portuguese lessons at another school.

The bilingual stream has also brought wider benefits, injecting new life into a school which had falling pupil numbers and was in danger of closure six years ago. Though the bilingual classes have yet to reach Year Six, the national curriculum scores of 11-year-olds taking the English curriculum have soared from significantly below average to average over the lifetime of the project. As more parents put Wix as their first choice or move into its catchment area, the proportion of children on free school meals has dropped from one-half to one-third.

Any fears that the standard of English and maths might be sacrificed to foreign language competency were dispelled when the first intake of French and English children took the national curriculum tests for seven-year-olds last spring and did better than those in the parallel English class. Next summer they will sit the national tests given to children in France a year later than in England.

Parents from Wandsworth apply either to the classic English stream, which takes around 30 pupils, or the bilingual class which has 14 places. The Lycée parents can also opt for the bilingual stream which is housed next door at Wix.

The French pay fees, even if their children are in the same class as the state school pupils. It is not an issue, says Paul-Marie Blanchard, the French head teacher: "French parents see it as a fantastic experience which is not just language but cultural, children learning from each other. We have a long waiting list."

The French curriculum is more structured than that in England but teachers are given more autonomy over the way they teach it, says Wolstencroft. "Paradoxically, the curriculum is more clearly defined but there is not the same tendency to micro-manage teachers. The French start off more slowly and don't teach reading and writing formally until Year Two but then the demands are stepped up more quickly."

Both the French and the English teachers have had to adapt to each other's way of working – the French more traditional talk and chalk and the English less formal and more creative. Sally Onions, the English classroom teacher, says the children swap from French to English with no difficulty when she takes over on Wednesdays. "If you look at their books, I don't think you would see any difference between the work of the French and English children. It's the finest job I have ever had and the most creative."