Mike Ullmann calls it "just a silly idea that I brought out at interview".
Applying to become head of languages in an under-performing department at a half-empty, debt-ridden state boarding school in Bishops Stortford, Hertfordshire, he suddenly suggested teaching other subjects in French.
"The idea was to raise the profile of languages in the school. I'd been on lots of exchanges and I'd always been impressed with the standard of language of youngsters abroad and felt there must be a way of improving standards here," he says. Many Continental schools he had visited had bilingual sections, but they were almost unheard of in England.
To Mr Ullman's surprise, the headteacher who was interviewing him seized on his idea. That was in 1992. Now, Hockerill Anglo-European college in Hertfordshire (school crest: a rampant English lion surrounded by the gold-on-blue stars of the EU flag) is recognised by the Office for Standards in Education as one of the most improved schools in the country.
Most of the pupils in Years 8, 9 and 10 study history and geography for two years in French. They travel at least three times a year to France and spend between two and three weeks attending schools there or in francophone Belgium, and do work experience overseas. The only disappointment is that they have to revert to English to take their history and geography GCSEs (the school is lobbying exam boards to change this). Sixth-formers take the International Baccalaureate, many of them as fully bilingual students.
Results have risen dramatically, from 48 per cent obtaining five or more A*-Cs at GCSE in 1999, to 85 per cent last year; and from 44 per cent obtaining the IB (13 per cent the bilingual version) in 2000, to 95 per cent (55 per cent bilingual) last year.
Mr Ullmann helped to introduce the section bilingue, which began Hockerill's transformation in results and identity. It became an Anglo-European college after its governors opted to change to grant-maintained status in 1994 and, since 1998, has been a specialist school for languages. "The international dimension has been at the core of the college's development," says head Robert Guthrie. "It's what makes us unique and it has a very strong resonance with a lot of parents."
Mr Ullman adds: "The challenge was convincing parents, the children and particularly the rest of the staff. We were treading on the toes of the history department. But, amazingly, people responded brilliantly. And from the earliest days it attracted attention, which was what the school needed badly."
There are several ways of setting up a section bilingue. Some involve using French for part of the course, or part of each lesson. Hockerill opted for total immersion, where no English is spoken in lessons. Pupils receive intensive French tuition for their first two years, backed by exchanges with partner schools in France, where they attend lessons for a fortnight in Year 8.
By Year 9, they are ready for the boldest move: the strongest linguists are taught history and geography entirely in French for two years. "We didn't have the teachers at first," Mr Ullmann says. "I taught history because it was an interest. Now we're established we can employ teachers who are fluent French speakers."
At first, around 30 per cent of the year group took history and geography in French; now it's around 80 per cent. A German section has been added, and some students even take a module of science in French. Most pupils now take GCSE French at the end of Year 9 and start on AS and A2 in Year 10.
History and geography follow the usual curricula, but a different perspective inevitably creeps in. For instance, Mr Ullmann says of the Treaty of Versailles, signed at the end of the First World War: "The British, American and French view is very different from the German."
Dr Guthrie argues that because students have to maintain concentration in order to speak a second language, they also focus harder on the subject they are studying in a foreign tongue. There can be a teaching benefit, too. Dr Do Coyle, vice-dean of the school of education at Nottingham university, whose trainees take their practice at Hockerill, says that bilingual teaching has stimulated her students' intellectual development.
"Language classes tend to be more functional, about managing to get things done or buying things," she says. "This is on a completely different intellectual level and challenges them in a different way. It makes them understand that language isn't just what you need when you're shopping in Spain, but a medium for learning.
"Hockerill is one of the leaders in the field in the UK. They've managed to show that students don't fall behind in their subject areas, which is clearly a concern. Oddly enough, the subject can even be more accessible in a foreign language because you might not give such consideration to your presentation in English."
Dr Guthrie says the school's approach has improved pupils' attitudes: "The fact that they're doing something different and successful, in some cases has transformed them and given them higher expectations of what they're capable of doing across the board. That is the seed of all our academic achievement."
And he goes further, saying the culture of experimentation and risk-taking has permeated the school's professional practice and given it an international reputation. Visitors have included the French and German ambassadors; there are around a dozen language assistants (four from France), many of whom live on site; and boarders now come from across the world.
Dr Guthrie says this international mix at Hockerill is as important as his pupils' overseas experience. He encourages it with advertising for boarders in the foreign press (the Government pays the tuition tab for anyone with an EU passport, so the pound;7,000 boarding fees are a third of the cost of private schools' fees).
All this adds up to a school population above the national average in prior attainment and socio-economic background. Nevertheless, Hockerill does a remarkable job in pushing results into the top 5 per cent nationally: Ofsted calls it one of the top schools for "value added", with standards well above similar establishments.
Hockerill has links with schools in Italy, Spain, Japan and Romania and wants to move beyond exchanges to working on joint curriculum development, with pupils carrying out projects with students at Coll ge Ste Veronique in Li ge, Belgium.
Dr Guthrie's conclusion is that learning to speak another language fluently gives pupils the confidence to communicate across borders, which will be vital for the workers of the future. "Having an international outlook has got to be at the core of the best sort of liberal education," he says.