The number of students in Wales gaining top A-level grades has fallen for the second year in a row, figures published yesterday reveal.
In this year's exams only 23.9 per cent of entrants gained A grades, down from 24.4 per cent last year and 25 per cent in 2009.
The figure is now the same as it was in 2006 and is well below the UK-wide figure, which remained at 27 per cent.
In addition, only 6.3 per cent of students gained A* grades, down from 6.5 per cent last year and lower than the UK figure of 8.2 per cent.
Leading academic Professor David Reynolds, a policy adviser to the Welsh Government, said the "inferior performance" of Wales's top students compared with the rest of the UK was "particularly worrying".
He said: "Just as with last year's Pisa results, it is the most able pupils in Wales who are now delivering the worst performance, which is an extraordinary state of affairs given our educational history of being more successful for our most able pupils than our less able.
"There is nothing that suggests any ray of hope in these figures, which provide further evidence to support everything that (education minister) Leighton Andrews is trying to do to improve the education system."
But Gareth Pierce, chief executive of exam board WJEC, suggested the decrease in the top grades may be linked to the 1.5 per cent increase in entrants this year, and specifically a 3.3 per cent rise in the number of entries by boys.
Mr Pierce said: "Boys' outcomes are generally slightly weaker than girls', so I think that could be a factor. However, I think the results emphasise how important improvement initiatives are at all stages, including post- 16.
"It may be that we need to remind ourselves of the need for post-16 education to have as much attention given to it as earlier key stages."
Although the overall A-level pass rate (A*-E) has picked up slightly (by 0.1 percentage points to 97.2 per cent) after falling for the first time in a decade last year, it is still below the overall UK figure of 97.8 per cent.
Education minister Leighton Andrews called the A-level results "excellent" and said: "I want all young people in Wales to succeed to the best of their ability.
"There can be little doubt that the competition for university places, work placements and jobs is tough and getting tougher. These young people collecting their results today have taken the first steps towards securing their futures."
The skills-led Welsh Baccalaureate qualification continues to go from strength to strength after being rolled out to a further 3,000 candidates in the past year, and the percentage of students awarded the advanced diploma increased from 81 per cent to 83.5 per cent.
Mr Andrews said it is clear that the Bacc is quickly becoming embedded as the "pathway of choice" in Wales.
Mr Pierce said the continued improvement showed the "substantial efforts" schools and colleges have put into the Bacc, which is a "challenging" qualification to deliver and complete.
Meanwhile, the Government said it is keen to share the good classroom practices that have brought about "significant improvements" in this year's teacher assessments at key stages 1, 2 and 3.
The percentage of pupils who achieved the core subject indicator (CSI) - at least the expected level in English or Welsh, maths and science - increased at all key stages.
The increase was particularly notable at KS3, where 68 per cent of pupils achieved the CSI, compared with 63.7 per cent last year.