The number of A-level students awarded A grades or higher has fallen for the first time in more than 20 years - but the overall pass rate has gone up.
A total of 26.6% of grades received by students in England, Wales and Northern Ireland this year were A or A*, down on 27% in 2011.
But the cumulative percentage of grades from A* to E - which constitutes a pass - increased slightly from 97.8% to 98%.
And for the first time since the A* grade was introduced in 2010, boys outperformed girls in achieving the top grade, by 8% compared to 7.9%. The overall number of A* grades fell from 8.2 to 7.9%.
It comes after, in an attempt to tackle grade inflation, regulator Ofqual told exam boards this year they would be asked to justify results that differ wildly from previous years.
This year's students will also be the first to face higher tuition fees of up to £9,000 a year.
Chief executive of the largest of England's three exam boards, the AQA , Andrew Hall told Sky News he did not believe the fall in the A grade percentage was the result of efforts to tackle grade inflation.
"What you've got is some very interesting things happening this year," he said.
He said the profile of A-level students had changed as more had stayed on in education after recognising the qualifications' importance and related employment opportunities.
He added: "I'm very, very clear in my own mind that the grades have been awarded by AQA, and I'm sure the other boards, in exactly the same way we've always done it. I personally do it in AQA, so I absolutely know that."
Professor Alan Smithers , director of the Centre for Education and Employment Research at the University of Buckingham , told Sky News that the "narrative" had changed for examiners this year.
"I think the subjective view for examiners had previously been that results should be like the previous year, but a little bit better," he said.
"This year we have had the new watchdog, Ofqual, which has said it believes there has been an inflationary element and that examining boards will have to account for any major deviation in results, upwards or downwards.
"The Government has also been saying, 'These A-level results are not quite believable.' So overall, the message going out to examiners has been, 'be tough.'"
He added that the trebling in the number of A grades awarded over the last three decades had made it difficult for universities to distinguish between top students.
Among those receiving A-level results was British Olympic bronze medallist, diver Tom Daley .
He tweeted: "I got an A in Spanish! Overall I have A* photography (A2), A spanish (A2) and A maths(AS) :) thanks 2 @PlymouthColleg1 :D."
Many of the hundreds of thousands of students receiving their exam results will be hoping to make the grade to secure a place at their university of choice.
A total of 357,915 students had been accepted onto university courses before receiving their results this year, down almost 7% on 2011, UCAS figures show. The total number of applicants was down from 681,593 in 2011 to 629,140 this year.
However, changes to the admissions process means universities will be able to admit as many students as they like who achieve the top grades of two As and a B, or higher.
It means they will be able to offer last-minute places to those who do better than expected and meet this threshold.
Brian Lightman, general secretary of the Association of School and College Leaders (ASCL) , said: "When you are talking about those sorts of high grades, A and two Bs, people scoring those sorts of grades - for those to be disheartened would be a tragedy and we must do everything we can to enable them to get their place.
"My advice to students would be don't give up, to look at the options that are open, and there are still plenty of opportunities out there."
