An exam often described as a tougher alternative to GCSEs, which is popular in the independent sector and will become available in state schools next month, is producing the best grades of any major academic course in the UK, The TES can reveal.
Some two-thirds of all pupils entered for International GCSEs from UK schools last year achieved an A* or an A, with more than one in three entries gaining an A*. The A*-C pass rate was well over 90 per cent, figures analysed in detail for the first time by this newspaper show.
In two popular subjects - biology and physics - offered by the larger of the two boards, more than half the grades awarded were A*s.
These statistics are far in excess of the national GCSE figures, where two in three candidates achieve A*-C. This is to be expected, given that only private schools, many of them highly selective, have been able to take IGCSEs until now.
But IGCSE success rates are also significantly better than those achieved by independent schools in conventional GCSEs, data from the Joint Council for Qualifications show. The number of pupils getting A grades at IGCSE also exceeds the number of pupils from independent schools getting As at A-level.
Alan Smithers, director of Buckingham University's Centre for Education and Employment Research, said: "These figures are staggeringly high. Of course, it is only a sub-group of the overall school population that is taking these exams. But they are very interesting."
The statistics were released by Edexcel and University of Cambridge International Examinations (CIE), the two IGCSE boards. Edexcel's figures for the years 2006-09 are available on its website, but have been subjected to little scrutiny and are not published alongside national GCSE results, which will be released next week for 2010.
CIE, which is thought to have a smaller share of the market than its rival among UK schools, does not publish figures for these schools, but released key elements of its data after a request by The TES.
Edexcel's data for candidates from UK schools show that the exam's popularity has soared, with entries growing more than fivefold from 7,528 in 2006 to 37,154 in 2009. This means there were almost as many entries from UK candidates last year as from the rest of the world, with candidates from overseas contributing 43,017 entries.
Subject-by-subject figures for 2009 show that in biology 53 per cent of grades were at A* and 82 per cent were awarded A* or A. In physics, 51 per cent got the top grade with 80 per cent achieving at least an A.
In maths, the most popular subject, 39 per cent got the top grade and 71 per cent either an A* or an A.
Overall, 39 per cent of entries with Edexcel gained an A*, 69 per cent either an A* or an A, and 94 per cent A*-C.
Traditionally, marks awarded in most exams have followed a "bell-shaped" curve, with most pupils gaining the middle grades and fewer doing very well or very badly. Edexcel's IGCSE results for UK candidates, however, follow a different pattern, with A* the most commonly awarded grade, followed by A, followed by B, and so on down to G grade.
The improvement of results in Edexcel's IGCSEs has also followed the pattern of GCSEs and A-levels: comparing the data from 2006 and 2009 shows that the proportion of entries gaining the top grade has increased.
Entries are dominated by maths and science subjects, with English, humanities and languages registering comparatively few candidates.
More boys than girls were entered for Edexcel's exams, which may reflect their popularity with prestigious private boys' schools, including Eton, Winchester and Harrow. Boys also performed slightly better than girls.
Candidates from UK private schools also easily outperformed their peers from overseas. Of international candidates taking Edexcel's IGCSEs, 16 per cent got A*s in 2009, 37 per cent achieved A* or A and 78 per cent gained A*-C grades.
CIE's figures show that 33 per cent of UK candidates gained an A* last year, with 61 per cent achieving A* or A and 92 per cent scoring A*-C. The subject with the best grades was chemistry, where 47 per cent of entries were at A*, and UK candidates again did much better than the worldwide average.
Scrutiny of the take-up of CIE exams in the UK is impossible as the board refused to reveal the entry figures, citing commercial confidentiality.
CIE did, however, release the results of students in selected other countries and these showed that pupils from China outperformed their UK counterparts at A*, with 38 per cent of entries from the country given the top grade.
The Joint Council for Qualifications data shows one in four independent-school pupils entered for mainstream GCSEs gained A*s in 2009; 54 per cent of these entries were at A* or A and 92 per cent were at A*-C.
The figures are likely to provoke interest in the state sector. Maintained schools were banned by the Labour government from offering the IGCSE, with the argument being that the courses did not follow the national curriculum.
The new Government has reversed this decision, and schools will be able to start teaching at least CIE's IGCSEs from next month. Some 60 schools have reportedly registered interest in offering CIE's version of the exams.
They will be aware of the publicity that IGCSEs have had, most of it implicitly favourable. Last year, Manchester Grammar School became the first well-known institution to abandon mainstream GCSEs altogether, arguing that those launched last year were "not challenging".
Private schools in general have often argued that the IGCSEs they have opted for are more stimulating for their pupils.
The science IGCSE has been widely reported as offering a tougher, more traditional scientific experience. Richard Pike, chief executive of the Royal Society of Chemistry, has been among those speaking up in favour of the international version recently.
But the IGCSE in maths might concern traditionalists because, unlike the GCSE, pupils do not have to show they can answer questions without a calculator. (see box). Pupils taking Edexcel's French and German IGCSEs are not assessed for their speaking skills unless they choose to have these certified.
Mary Bousted, general secretary of the Association of Teachers and Lecturers, said: "A detailed look at the IGCSE is long overdue. IGCSEs have been promoted as a symbol of rigour, but no one seems to ask whether or not they really are. The IGCSE should be rigorously looked at to ensure that it is a fit and proper qualification for the 21st century."
Geoff Lucas, secretary of the Headmasters' and Headmistresses' Conference, which represents 250 leading private schools, said that heads he had spoken to had not said they chose IGCSEs because of the good results.
Asked why the grades were significantly better even than GCSE success rates at independent schools, he said: "There are some possible explanations. One is that (IGCSEs) are easier, but that does not hold water.
"The other is that they are taken by a very selective intake at the moment. I would say that when schools first started using them, they were doing so for bright kids for whom it was felt that GCSEs were not sufficiently challenging.
"Even if that does not explain these grades, if the course is more stimulating and the kids are responding to that, you are going to find more of them doing well. That is a good model for how an exam should work."
Professor Smithers said the IGCSE's grade profile may be explained by the fact that very successful, highly selective private schools have tended to take it.
"The issue is how can we be sure what these grades mean, and how they compare with GCSEs? It is something for Ofqual to look at, I think," he said.
Regulation has been a pressing question this summer. Indeed, it has cast doubt on whether state schools will be able to offer Edexcel's version of the exam from next month, as ministers intend to do.
Edexcel's IGCSE has, until now, not been regulated by Ofqual. Surprisingly, a spokeswoman for the regulator said exam boards had to choose to seek "accreditation" from Ofqual for each of their exams in order to be regulated by it.
Cambridge Assessment has sought accreditation in the past for its IGCSEs and they are now regulated. However, Edexcel appears to have been caught on the hop by the new Government's decision, announced within a month of it taking office in June, that the IGCSE was to be made available in state schools from the coming academic year.
Commenting on the Government's decision to make IGCSEs available in state schools from 2010, an Edxcel spokeswoman said: "It was not something that we were necessarily aware would happen quite so quickly."
Edexcel's exams are now being considered for accreditation by Ofqual. Ministers seem unwilling to allow them to be taught in state schools until they are accredited, but an Ofqual spokesman would not say whether they would be accredited by next month.
Edexcel's spokeswoman said: "They are in for accreditation, and we are expecting them to come back. We are hoping that they will be accredited before the start of term. There are options if they do not come back by then.
"We either hang on and go for a 2011 launch or we put out some information on rough specifications so that schools can start teaching the subjects (in advance of accreditation)." Of the second option, she added: "We would prefer not to do this if we can help it."
A Department for Education spokesman referred The TES to the Government's press release from June, when it said CIE's IGCSEs had been approved for use in state schools and that the "remainder" - Edexcel's - would be subject to accreditation by Ofqual.
This looks like another example of the Government proceeding at great speed in its early months. But whether the new freedom for maintained schools to choose IGCSEs comes in straight away for both versions of the qualification, or somewhat later for Edexcel's, its impact on state education will be interesting to observe.
Next week: BTECs
The same, but different
Maths GCSE and IGCSE: a comparison
So what is the difference between the exams set for IGCSE and for GCSE?
A close look at specimen papers offered by Edexcel for the most popular IGCSE subject, maths, offers some pointers, although the differences are subtle.
In fact, comparing specimen IGCSE papers with one from Edexcel's "linear" (non-modular) version of the GCSE, it was difficult to tell them apart.
The IGCSE requires students to take two exams of two hours each, both of which allowed calculators.
The GCSE has two papers of an hour-and-three-quarters, for one of which calculators are barred.
I tried specimen papers, calculators allowed, from both exams, and found the questions of a similar standard of difficulty. The only difference I could spot was that for the GCSE, short written answers were required for the occasional question. This was not the case for the IGCSE paper.
This difference may reflect the only disparity between the "assessment objectives" of the two exams: the GCSE features questions on "using and applying mathematics", including communication - alongside problems on number and algebra; space, shape and measures; and data handling - while the IGCSE does not.
If anything, I think the writing element and the barring of calculators from one paper probably made the conventional GCSE slightly harder. Of course, it is impossible to judge how hard it would have been to achieve a good grade on these papers without seeing the number of marks needed for each one. These are not routinely published.
One major difference in the past may help explain the IGCSE's popularity with independent schools: the fact that it does not feature coursework.
Up until courses ending in 2008, mainstream GCSEs did include coursework. This was not widely loved in the subject, and was scrapped in 2007, leaving these two exams now looking, to this observer, fairly similar.