"So you do the IGCSE in your school?" Welcome to the latest question to be popped by private school pupils to their state school peers.

To which the answer is usually, "No. What's that?" accompanied by a look of mild bewilderment. Even the most savvy of state school students have been unaware, until quite recently, that there are exams, similar in character to the ones they are taking but apparently "far more challenging" in quality. Given these sorts of exchanges, the news that private schools are increasingly shunning traditional GCSEs in favour of the international GCSE and that within two years one-fifth will offer the international baccalaureate (an alternative to A-level) come as no surprise to those who still fraternise across the state/private divide.

Shared discussion of the stresses of public examinations, once a relatively safe, even amicable area of conversation, have in recent years given way to the strained drawing of distinctions or, in the odd case of unpardonable bad manners, the less pleasant kinds of one-upmanship.

Demoralising? I'd say so. At least on a human level, where real teenagers slog away for months and years on end, note taking and mock taking and the rest – only to be told that however hard they work and however successful they are, their results are demonstrably of lesser value, according to the calculations of a parallel private system. Ten A-stars, but not an IGCSE among them? Oh, what a shame.

More worrying still, the argument for these exams is increasingly justified on the grounds that employers and universities need to be able to distinguish the truly talented from the merely well drilled and diligent. Forget the sillier forms of intellectual snobbery. State school students risk being at a serious disadvantage when it comes to applying for certain universities and jobs.

So what else is new, you might ask? The emerging distinctions in public exams is just the latest piece in a much bigger jigsaw, a depressing new element in a system that confers numerous specific advantage on a tiny percentage of the already privileged, be that smaller class sizes to more individual attention, a broader curriculum or separation from the mass of society.

In fact, the exam gap is relatively easy to address. The government, exam boards and qualification authorities should between them reach an agreement on universality. They should abandon what John Dunford has called the "smorgasbord" of differing qualifications, and create a system that applies to all children, with built-in ways to distinguish, as universities and employers may have to do, between the truly talented and the merely well drilled and super diligent. Why not revisit the sound principle of the Tomlinson inquiry, which suggested a single overarching diploma that contains within it different components, both vocational and academic, and rising levels of achievement within both of these?

This is a far fairer approach than saying, as Michael Gove has done, that the Tories will introduce the IGCSE in certain state schools – a promise that threatens to create yet more unhelpful sub-hierarchies within the state system. His prescription may be wrong, but Gove is right to challenge the state/private division on this matter. As he says, it is vital that "children from state schools are able to trade in the same exam currency as their wealthier peers ... and compete on a level playing field".