GCSE results 2013: Your reaction
There is a drop in the proportion of GCSE exam entries awarded a C grade or above, for the second year in a row.
More than 600,000 teenagers in England, Wales and Northern Ireland are receiving results, with head teachers saying changes have caused "a lot of turbulence" in grades.
BBC News website readers and Twitter users are reacting to the news of their GCSE results.
Charlotte Laycock, student in Stalybridge, Greater Manchester
I got As and A*s in my mocks but this still came as a shock.
I was a bit worried when I heard the grade boundaries had been changed but I have never been borderline in any subject, so it didn't really apply to me.
But it's a relief to know I haven't been caught out by it.
I'm the eldest of three so I'm setting an example.
I think a lot of my friends did better than they expected too.
I think if anything knowing about the grade boundaries made us work harder.
Ben Nicholson, student in Durham
I collected my GCSEs today which included two A and four B grades.
I am over the moon.
I went to school at 10:30 to open my results.
I was very nervous beforehand.
My mum was really proud. Took us to the fish and chip shop to celebrate.
I had a jumbo sausage, chips and a can of diet coke.
Natascha Lonnecker, parent in Swindon, Wiltshire
My kids took their IGCSE this year (we are home schooling).
My son, aged 12, got a B in English and A* in chemistry.
My 15-year-old daughter, who took her first exam when she was 10 (German A*) took her last remaining exams in English, maths and chemistry. She achieved A* in all of them.
We also noticed that the IGCSE changed their format making them harder compared to previous versions, although luckily we managed to cope with it.
Personally I am very proud of my kids' achievements.
My daughter taught herself physics GCSE last year and achieved a B.
My daughter will go to a local school part-time to do biology AS next year and will teach herself German AS level at home as well as teaching my son.
I want her to go to university at the same time as everyone else.
Natalie - @_natalieegan - tweets: Most people I know are content but definitely a few unexpected lower grades from myself and others
Brogann - @Alex_T_Brogan - tweets: got 11A* and 5As! 912 GCSE points, best at my school!
Sam Kenward - @SamKenward - tweets: I'm very pleased with my results. I got 5A's, 3B's, 4C's and a merit in ICT!
Callum Pope - @callumpope - tweets: happy with results, but have a raging headache and being sick! Ah well, the celebrations can wait!
Ruth Buckley - @RuthBuckley88 - tweets: at the age of 25 finally achieved my maths GCSE! Chuffed to bits!
Georgia Occomore - @GeorgiaOccyRose - tweets: out tonight to celebrate my GCSE results and mum and dad's anniversary :)
Adrian Dowling, parent in Colwyn Bay, North Wales
My son did single subject science and got A*s in his physics, chemistry and biology mocks.
He worked really hard and did a lot of revision. He ticks all of the boxes as a model student in that respect.
He knows what his weaker subjects are, he's not so fond of English, but in sciences he has always been very strong.
He got an A for science but a B for additional science. We don't even know what this 'additional science' grade is for.
We just can't understand it. Then when I heard they had changed the grade boundaries, I wondered whether that had had any impact.
It seems people are so obsessed about statistics and results, but no-one wants to take the time to explain how they arrived at that conclusion.
He wants to do maths, physics and chemistry at A-level. He should be celebrating today, because he got five As and an A* in history, but instead he's just confused and disappointed by the B in this unknown additional science.
I got mine today; 3 A*s - physics, chemistry and German; 4 As - maths, biology, French and music; and B in English language and literature, as well as in history. Unsurprisingly, I failed additional maths - we did a 12 month course in about 5 months - but that was done simply as preparation for A-level maths. Just as unsurprisingly, the best person in my school got 7 A*s, and I think 5 As, and it was a girl. Henrik Oldcorn, Devon
10 A* grades! It was so unexpected, my legs turned to jelly as I opened the envelope! With GCSE grades set to be an even bigger determinant in university applications in the future, my dream of Oxford was hanging in the balance as I opened it up. But now I'm so pleased! Oliver Northover Smith, Pyrford, Surrey
Pleased with my results but my science is significantly lower than expected. Thomas Jelves, Trowbridge, Wiltshire
One mark off an A grade for science! I'd of had an A* but due to the boundaries I am now only coming out with 79 when I needed 80 for an A! Utterly devastated!! Sending it off for remarking as many others I know are! Laura Howell, Southport
I got my results today and I'm over the moon with them! 7A*s 3As and a B. Alexander Bailey, Morpeth
I achieved better grades today than I ever could have hoped for, but the feeling of elation was overrun by the sympathy for others who had not lived up to the expectations that people around them were holding. There is too much pressure placed on the 15- and 16-year-olds in this country. No other country places such emphasis on this stage of your life and how much it can potentially affect you in later life. Ed Metherell, Bristol
Interviews by Victoria Park