Independent schools in Wales are dropping the GCSE for its international cousin - even though the qualification is not officially recognised in the UK.
International GCSEs are accepted across the world, but few state schools offer them because they are not Government funded.
This year, the Independent Schools Council recorded a large rise in IGCSE entries among its Welsh members, from 19 in 2007 to 125 in 2008.
With more study options and less coursework, the international qualification, which has been examined for over 20 years, is viewed by some teachers as a more rigorous qualification.
St Gerard's School in Bangor, whose pupils performed well in this year's GCSEs (see arrow, right), entered its whole Year 11 cohort for IGCSE double and triple award science in June.
Anne Parkinson, its headteacher, said her science department felt the starting level of GCSE science was too low, which meant pupils repeated lessons they had already learnt in Year 9 and more able students were not being stretched.
But Miss Parkinson said it was also important that the qualification did not disadvantage less able pupils. "The general view was that the IGCSE offered a better preparation for anybody going to continue with science at A-level or universities," she said.
After a successful start, Years 10 and 11 pupils at St Gerard's will continue to study the IGCSE, although Miss Parkinson said it was too early to tell whether results had improved overall.
Rydal Penrhos, an independent boarding school in Colwyn Bay which also reported good GCSE results, offers IGCSEs in maths, science and languages to overseas students who will go on to study the international baccalaureate.
Although the course has been successful, Tim Cashell, deputy head, said it was not open to UK pupils because of uncertainty over reactions by governors, parents and the wider community.
But the major concern for independent schools is that the qualification is not recognised by the Qualifications and Curriculum Authority and cannot contribute to a school's league table position.
"I am aware of a number of high-profile schools that have changed (to IGCSEs) and take pride in the fact that they are now at the very bottom of the league tables," Mr Cashell said.
There is a growing movement in favour of the IGCSE in the UK. Cambridge International Examinations, which offers the qualification, is in discussions with the QCA over official accreditation.
But their efforts have been hindered by a 2006 QCA report comparing GCSEs and IGCSEs, which concluded that the latter did not conform to the Government's key stage 4 specifications.
Percentage of pupils from Welsh independent schools gaining five or more top grades this year:
(Schools marked with * also offer the IGCSE in some subjects)
100 Haberdashers' Monmouth School for Girls; Monmouth School; The Cathedral School Llandaff; Westbourne School, Penarth; Howell's School, Denbigh; St Clare's Convent School, Porthcawl; St John's, Porthcawl; Netherwood School, Saundersfoot
98.82 Howell's School, Cardiff
97.73 *St Gerard's, Bangor
96.67 St Michael's, Llanelli
96.83 Rougemont, Newport
95.83 *Rydal Penrhos, Colwyn Bay
95.24 *Christ College, Brecon
92.86 St John's College, Cardiff
88.57 Llandovery College
85.71 Kings Monkton, Cardiff
Source: Independent Schools Council and school websites.