The number of A and A* grades awarded to this year's A-level students has fallen for the second year in a row, official figures revealed on Thursday.
The proportion of top grades awarded is believed to be the second biggest fall in the history of A-levels, after the pass rate fell for the first tim in more than 20 years last year.
In total, 26.3% of entries scored an A or A* this year, down from 26.6% in 2012 - a drop of 0.3%.
The latest drop comes amid rising numbers of teenagers taking A-levels in science and maths.
It had previously been suggested by some that an increased focus on traditional subjects, such as maths and science, could fuel a slight drop, as youngsters who may not have considered taking these subjects in the past, and may not be as strong in them, are now opting for the courses to help their chances of securing a university place.
In total, biology, chemistry and physics accounted for 17.8% of all entries - up from 17% last year and 15% in 2009, according to figures published by the Joint Council for Qualifications (JCQ).
And one in eight (12%) of entries were for maths or further maths, up from 11.5% last year and 9.8% five years ago.
There were almost 24,000 more entries for the sciences this year compared with 2009, JCQ said, and nearly 19,000 more for maths courses.
The new statistics also show that the number of entries awarded an A* - the very top grade - also dipped this year, with 7.6% of exams scoring the mark, compared with 7.9% last year.
The overall A*-E pass rate has risen slightly by 0.1%. Some 98.1% of exams achieved at least an E, compared with 98% last year.
More than 300,000 students in England, Wales and Northern Ireland are receiving their A-level results this morning.
For many, success in the exams will mean a prized place at university, an apprenticeship or other training scheme, while those who achieved less than expected are likely to be considering their options.
The national picture shows that boys have outperformed girls in the very top grade again this year, and widened the gap, with 8% of boys' entries attaining an A* compared with 7.4% of girls.
Girls are still slightly ahead in A*-A grades combined, but their results dropped half a percentage point this year to narrow the gap between the genders.
Overall, 26.6% of girls' entries got at least an A grade, compared with 27.1% last year, while 26% of boys' exams achieved this standard, up from 25.8% in 2012.
A-level economics is seeing a surge in popularity, the figures suggest, with 26,139 entries this year. The number of people taking the subject has risen by 50% since 2007.
But young people continue to turn their backs on many modern foreign languages, with both French and German entries down again this year. The numbers taking Spanish have risen by 4.1% on last year.
JCQ director Michael Turner said: "The continued rise in subjects such as the sciences, mathematics and the extended project, will be welcomed.
"However, that so few students take a language A-level is disappointing and, although Spanish continues to show growth, the overall trend remains downwards."
He added: "A huge amount of hard work and commitment has gone into achieving these results and we should all join in congratulating students across the country and wish them well for whichever path they choose next."