Educationalists have called for an investigation into why the number of students gaining top A-level grades has fallen for the second year in a row.

Last week’s results showed that, despite a slight increase in the overall pass rate in Wales, the percentage of pupils gaining A* grades fell from 6.5 to 6.3 per cent, and A grades were down from 24.4 to 23.9 per cent.

Education minister Leighton Andrews defended the performance and said the results did not take into account the skills-led Welsh Baccalaureate qualification.

Almost 7,000 students gained the Welsh Bac advanced diploma this year - the equivalent of an A-grade A-level - and Mr Andrews said the qualification was not always appreciated and should be included in the overall figures.

The minister attacked BBC Wales as “cynical” when it questioned him over the drop in top grades, despite the fact he highlighted the trend as a cause for concern in his landmark speech in February.

But the Conservatives accused Mr Andrews of “denying the obvious”, and said there must be an evaluation of the situation and a “reasoned discussion” about why top grades had fallen.

The Liberal Democrats called the situation “worrying” and said it was further evidence that the underfunding of the education system was having an impact on achievement.

Dr Philip Dixon, director of education union ATL Cymru, said: “I think we need to look calmly and soberly at the decline in the top grades and ask a whole range of questions as to why this is the case.

“Are we entering too many youngsters for A-levels when they should be taking other qualifications? Also, is the percentage of children in independent education in England skewing the stats?

“Even though the decline is slight, we have got to allow our best students to excel. There’s no merit in neglecting the top end,” Dr Dixon added.

Professor David Reynolds, a policy adviser to the Welsh Government, said the “artificial row” was unhelpful.

“We want Welsh students to have the competitive edge that the Bac gives them and for it to count as an extra A grade, but we also want A-level results to improve at the same time,” he added.

“We need to look at why that is not happening. Perhaps there’s a logic in creating a merged assessment system that takes all the qualifications into account.”

That view was backed by Careers Wales, whose chief executive Trina Neilson said the Bac must be given parity of esteem with A-levels, which are no longer “the only game in town”, and added that the “A* culture” must be challenged as a method of selection.

“With the increasing divergence of education policy in Wales from the English model, employers and education institutions will inevitably begin to find that applicants have different types of qualifications from different institutions,” she said.

“They must learn to recognise the achievement of the students and potential employees rather than remain wedded to selecting those applicants who have three or four A-levels of grades A* to C.”