There was a striking disparity between two sets of figures published, to varying degrees of media interest, in the past two weeks.

The first, which garnered front page headlines in the Daily Telegraph, showed how independent schools have pulled further ahead of their state rivals at the top end of A-level performance in recent years.

The proportion of A grades improved by 3.9 percentage points to 20.4 per cent in comprehensives between 2002 to 2008. The corresponding rate in private schools rose by 9.1 points to 50.4 per cent over the same period.

But for GCSEs, the position was very different, although this struggled to gain much attention in the national dailies, with only The Independent and The Guardian mentioning it.

In fact, comprehensives have closed the GCSE performance gap on independents at both A* and A grades and, more strikingly, at C grade, the new figures show.

Over the past six years, the proportion of state entries attaining A*-C rose by 8.9 points to 62.4 per cent, while in private education it fell by 0.4 points to 90.4 per cent.

So what has been going on? Why are two measures of performance pointing in such radically different directions?

The examination boards were unwilling to offer any explanation, saying that their job was simply to produce the figures, although they did suggest that research should be carried out into possible causes. But one hypothesis suggests itself. Schools in both sectors respond to the varying pressures they face by targeting resources where they think they will be most effective.

Private schools know that many parents will expect the fees they pay to help their child get into a top university. So they make a high grade at A-level their priority.

In the state sector, league tables and targets focus predominantly on the ability of middle-ability children to achieve a grade C.

Extra effort has undoubtedly been devoted to these pupils, as initiatives such as London Challenge, which gives additional attention to CD borderline teenagers, shows.

Will these children then go on and achieve A grades at A-level? It seems unlikely. But for the school, whose future may depend on securing good scores at GCSE, that may be less of a problem.

Top grades at A-level are the key to university entrance, and encouraging more working class children to go to good universities is a key Government priority in its drive to improve social mobility. The league table regime may not be helping.