Video report by ITV News Correspondent Stacey Foster
The proportion of A-level entries awarded an A grade or higher has fallen to the lowest for more than a decade, national figures show.
There were 801,002 A-levels awarded, down 1.3% on last year's total and the lowest number since 2005.
Girls narrowly clawed back the lead from boys in terms of A* and A grades, although boys still outperformed their female classmates in the highest result.
For the first time, there were more entries for A-level science subjects from girls than from boys.
The shift comes after a major push in recent years to encourage girls to study science and maths-based subjects.
Number of A levels awarded this year.
Spanish has become the most popular foreign language at A-level, overtaking French for the first time.
The figures, published by the Joint Council for Qualifications (JCQ), cover A-level entries from students in England, Wales and Northern Ireland.
Around 300,000 students are receiving their results on Thursday.
In total, 25.5% of UK entries were awarded an A or A* grade this summer, the lowest proportion since 2007 when it was 25.3%.
A* grades were introduced in 2010.
Before this, the highest result was an A.
UK students awarded an A or A* grade
The proportion of students receiving the top grade at A-level has increased slightly in Northern Ireland.
Those awarded an A* rose 0.6 percentage points from last year, and almost a tenth received the top grade. The rise was mainly driven by better performance from girls.
Thousands of students learned their results on Thursday morning.
Science entries by gender
Source: Joint Council for Qualifications (JCQ)
Girls - 84,111
Boys - 83,133
Girls are back in front in terms of top grades, with 25.5% of entries handed at least an A, compared with 25.4% of boys – a gap of 0.1 percentage points.
But on A* grades alone, boys performed better, with 8.2% of entries getting the highest result, compared with 7.5% of girls’ entries.
Girls are now more likely in general to take a science A-level than boys, the data shows.
For biology, chemistry and physics A-levels, there were 84,111 entries from girls this year, compared with 83,133 from boys.
The change has been driven by more girls than boys taking biology and chemistry.
But boys are still significantly more likely to take physics, with more than three times as many entries than their female counterparts (30,159 compared with 8,799).
In languages, there were 8,625 entries for Spanish A-level and 8,355 for French.
French has seen a decline in recent years, while Spanish has been increasing in popularity.
Dr Philip Wright, JCQ director general, said: “This year’s pass rates are stable across all A-levels and it is particularly encouraging to see the rise in young women being inspired to take science A-levels.
“For the very first time, female entries have overtaken male entries in science.”
Record number of entries for Spanish A-level
Ahead of results day, grade boundaries for two of England’s biggest exam boards, Edexcel and OCR, were leaked.
The documents showed that students needed to score just over half marks in A-level maths to win an A grade this summer.
Grade boundaries for Edexcel’s maths A-level show students who gained 165 out of a possible maximum of 300 marks (55%) will be awarded an A.
Separate documents show that those who took OCR’s A-level maths will get an A if they achieved 54% across all papers – a total of 161 out of 300.
Last year, 184 marks (61%) were needed for an A grade in Edexcel’s maths A-level, while for OCR the required mark was 197 (66%).
The figures relate to overall grade boundaries for new specification maths A-levels.
Practically all A-level courses have been reformed, with maths one of the last to be overhauled as part of a major revamp in England.
This summer is the first time grades for new specification A-level maths are being awarded to the vast majority of students.
The leaked documents also give grade boundaries for other A-level qualifications offered by Edexcel and OCR, and there are some differences between the two.
For example, 69% (208 out of 300) in an Edexcel English literature A-level achieves an A grade, while students taking the subject with OCR require 177 marks out of 200 (89%).