Girls have increased their lead on boys for top grades in GCSEs, in another record-breaking year of results.
More exam entries were given the top A and A* grades and just under 70% were awarded between an A* and a C grade.
The performance gap between boys and girls has now reached its the widest ever - 6.7 percentage points - at the top grades of A* and A.
About 650,000 pupils in England, Wales and Northern Ireland are finding out their GCSE results.
Students in Scotland found out the results of their Highers and Advanced Highers earlier this month.
Details of the GCSE results show an increase, for the 23rd year running, in the proportion of entries awarded between an A* and a C grade.
A total of 69.8% of entries made that grade.
There were more A and A* grades awarded too - with 23.2% of entries making that grade, up from 22.6% last year.
But the overall pass rate (A* to E) dropped slightly to 92.7%.
Results show the continuing trend for grades in Northern Ireland to be highest, with England second and then Wales.
In Northern Ireland, nearly 75% of GCSE exams scored between an A* and a C grade. In England, 69% made that grade and in Wales 66% did so.
Boys dropped further behind girls at the top grade, with just 19.6% of their exam entries awarded A* or A, compared with 26.5% for girls.
Last year there was a difference of 5.7 percentage points and this year it is 6.7.
Andrew Hall, director general of AQA exam boards, said examiners were "scratching their heads" over the acceleration in the trend of two decades - especially as the gap is narrowing at A-level.
"There will be something there about boys and girls maturing at different rates," he added.
Results day also shows the trends for GCSE subjects, and this year saw an increase in the numbers taking individual sciences but a continued fall in numbers taking history, geography and modern foreign languages.
The number of pupils taking physics rose by 16.4% on last year, while chemistry was up 16.2% and biology 14.2%.
But the number of entries in both French and German dropped by 13.2%, and is now less than half the 2002 figure for both languages.
Spanish also saw a small decline, reversing the trend over recent years.
History and geography have also seen a drop in entries, with history entries down by about 2,700 (1.2%) and geography entries dropping by 13,800 (7.1%).
The government has brought in a new measure to try to reverse the decline in these subjects, which ministers say should be at the heart of a good education.
The new measure - called the English Baccalaureate - will show that a student has achieved a good GCSE pass (A* to C) in five key subjects including maths, English, a language, two sciences and either geography or history.
Jim Sinclair, director of the Joint Council for Qualifications, which represents the exam boards, said: "The rise of biology, physics and chemistry is welcome news, as is the increased performance in maths and English.
"However, the continuing decline of modern foreign languages and the growing divide in performance between boys and girls at the top grades are worrying trends."
Schools Minister Nick Gibb said: "Today we can congratulate thousands of young people as they collect their GCSE results... No-one should underestimate the hard work and application needed to gain GCSE qualifications.
"While it is encouraging to see the rising uptake in maths and single sciences, it is worrying that once again there are falling numbers studying languages. Through the English Baccalaureate, we want to make sure all pupils have the chance to study the core academic subjects which universities and employers demand."
He said the gap between girls' and boys' results was "a concern".
"It's happening across the world... but we do have to reverse it," he said, adding that improving the teaching of reading in primary school and raising behaviour standards would contribute to improving the situation.
Christine Blower, the general secretary of the National Union of Teachers, said: "GCSE results this year are outstanding and the hard work that has gone into them should be applauded.
"The fact that modern languages continue to decline, however, is disappointing, especially taking into account our place in a global society and economy."
But she criticised the direction the government was taking, adding: "For all young people to be able to reach their full potential, we need to rid ourselves of this idea that an education system familiar to those who attended school towards the middle of the last century is the only way forward."
For the first time, most courses this year were taken in bite-size chunks, although course work has been cut down and replaced with school-based controlled assessments.
But Education Secretary Michael Gove has said he wants this modular system to end and a return to exams being taken at the end of two years of study.
He says this will end what he calls a "culture of re-sits" and restore rigour to the exams system.
Teenagers beginning their GCSE courses in 2012 will do their exams under the new system - at the end of their courses.