Treorchy comprehensive might seem like an odd school for an experiment in bilingual instruction. Not one of its 1,500 pupils speaks Welsh at home.

But the headteacher, Bethan Guilfoyle - herself a native Welsh speaker from Carmarthen - considers Welsh a key skill for pupils. She knows they will probably seek work or training outside the Rhondda valley. But four out of five will stay in Wales, where fluent Welsh is now an advantage in many jobs.

So four years ago, the school in Mountain Ash started an experiment to boost Welsh language teaching. It employs a primary Welsh specialist to give intensive tuition to pupils in their last two years at the seven feeder primary schools. The keenest pupils are then encouraged to enter one of two bilingual forms on arrival at the secondary school, where they learn history, geography and religious education in Welsh, all subjects where the school happens to have Welsh-speaking staff.

Other pupils also benefit from the intensive tuition in their primary school, which gives them a boost for learning Welsh as a second language.

The scheme was singled out as an example of good practice in a recent report on the teaching of Welsh. Ministers are said to be watching it with interest.

Is the school selecting the brightest pupils for favourable treatment? Those in the bilingual stream are not necessarily the brightest, says Mrs Guilfoyle, although they have to be bright enough to cope. And they are getting no more favourable treatment than those who take Spanish in three years or pupils who receive extra help with their basic literacy skills.

The children are full of talents and enthusiasm, says Mrs Guilfoyle. But they are not naturally full of self-esteem. Since coming to the school nine years ago, she has been busy not just raising academic standards and introducing vocational courses, but also building links with the wider world of business and the arts and encouraging children to perform. The school has a flourishing orchestra and the annual concert is famous for both quality and length.

Sixty-five per cent of children now stay on into the sixth form, with one a year heading for Oxbridge. The proportion of pupils getting five good GCSEs, only 29 per cent a decade ago, has risen steadily and was 60 per cent last year.