England's exams watchdog says A-levels and the International Baccalaureate (IB) are broadly comparable but have significant differences of approach.
Experts had trouble with key aspects of the qualifications
The Qualifications and Curriculum Authority (QCA) said Mike Tomlinson's qualifications task force seemed to be favouring some sort of diploma.
So it was timely to consider "the main example currently in use in the UK".
Its study found that A-levels and the IB made similar demands on candidates, who achieved broadly similar results.
The QCA review was also motivated by government demands to include a broader range of qualifications in school league tables from next year.
What it is
The authority says the International Baccalaureate Diploma Programme, created in 1968, has "a number of staunch supporters in the UK who are vocal in declaring its qualities".
The International Baccalaureate Organisation (IBO) describes it as a demanding pre-university course of study designed for highly motivated students aged 16 to 19.
Its two-year international curriculum allows students to fulfil the requirements of their state education systems without being based on any one.
An "idealistic vision" underpinned the aim of having a common curriculum and university entry credential for students moving from one country to another.
As well as a traditional curriculum it includes theory of knowledge, creativity, action and service, and an extended essay.
"The IBO's goal is to educate the whole person and foster responsible, compassionate citizens."
Students study six main subjects - three or four at higher level, the others at standard level.
They are chosen from language, second language, individuals and societies - things such as business and management, economics, geography - experimental sciences, maths and computer science, and the arts.
A-levels, on the other hand, did not call for students to follow an overall programme and there was "little real guidance" on the programme of study even for each subject.
IBs are graded from 7 down to 1, A-levels from A down to E.
Comparing the two sets of qualifications was not easy, the QCA said.
"Indeed, such are the differences that some of the questions are almost impossible to answer."
So four subjects were chosen for comparison, with the aim of covering a range of traditional subjects in the curriculum: chemistry, English literature, history and mathematics.
The study was done by examiners in the various subjects and by university admissions experts.
Their findings were that A level and IB examinations were comparable in the demands they placed on candidates.
"There were some interesting subject-specific differences either in breadth or depth, compensated in each case by parallel differences in depth or breadth," says the QCA report.
Performances producing different grades at the top and the bottom were also comparable.
Some differences could not be reconciled.
For example, IB chemistry practical skills were assessed internally against prescribed criteria, whereas the A-level practical was an external exam.
"These very dissimilar methods of assessing the same range of knowledge and skills proved hard for all the reviewers to compare."
Other fundamental differences emerged.
The IB, for example, was "traditionally rooted in a concept of the educated person with which Matthew Arnold would probably have felt comfortable."
Arnold, the poet and critic, studied Continental systems in his role as schools inspector in an effort to improve educational standards in Victorian England.
A-levels, far from being a complete programme of study, were designed as "a set of single subject examinations which can be taken in combination with any other subjects or with none."
Other complications came from the modular nature of A-levels and the ability to re-sit modules, and the fact that the Curriculum 2000 changes, introducing AS-levels, had yet to bed down.
As a result the bottom line of the study is that its conclusions "remain useful insights not precise statements".
Mike Tomlinson's review group is due to publish a report in about a month's time.