The number of top GCSE grades has fallen for the second year in a row, after a drastic - and controversial - upheaval of the exams system, official figures have confirmed.
The proportion of GCSE papers awarded an A*-C grade has dropped 1.3 percentage points since last year, making it the biggest fall since the exams replaced O-levels 25 years ago.
Just over two-thirds (68.1%) of entries scored at least a C grade this summer, while the number of entries gaining top grades has also fallen by 0.5 percentage points - with 6.8% achieving a coveted A*.
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Girls continued to out-perform boys, scoring higher results at A* and A*-C across all subjects.
The dip in national results comes amid huge changes in the exams system and it is thought that a rise in pupils entering maths GCSE early or multiple times, changes to science GCSEs and an increase in pupils taking international GCSEs (IGCSE) in certain subjects have contributed to the falls in performance.
Last year's GCSE results day was hit by controversy following grade boundaries being raised for the June 2012 exams, but not for the January exams. 45,000 pupils went on to re-sit their exams. The debacle, which lead to Ofqual chief Glenys Stacey being interrogated by MPs, was described as a "gross injustice" to students.
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The latest statistics show a drop in the proportion of entries scoring at least a C in key subjects including English, maths and science. Earlier this year, exams watchdog Ofqual warned students to expect a drop in science grades due to changes in the syllabus - which have left students "completely confused".
In English, 63.6% of entries gained a C or higher, down from 64.1% last summer.
This comes amid a rise in the number of younger students taking GCSE English, the Joint Council for Qualifications (JCQ) said. This summer there were 61,000 more entries for the subject and of these more than two-fifths (41.9%) were from pupils aged 15.
In maths, 57.6% of entries scored an A*-C grade, compared to 58.4% in 2012.
JCQ said there had been "significant early and repeated entries" for maths, with more than half a million entries before the summer exams. While results for 16-year-olds - the age at which pupils usually sit GCSE exams - remained "virtually unchanged", there was a decline in performance among 15-year-olds - those who are taking the exam early.
There has been a 7.6 percentage point fall in the proportion of entries awarded a C or higher in GCSE science.
It follows a move by Ofqual to toughen up the qualifications after a 2009 report by the regulator found that the courses were too easy. This is the first summer that results have been given for the revamped GCSEs.
More pupils were entered for the three separate sciences - biology, chemistry and physics - but there was also a drop across the board in entries scoring decent grades. In biology, 89.8% of entries got at least a C, down from 92.6% last year, in chemistry 90% of entries scored A*-C, down from 93%, and in physics 90.8% reached this standard, down from 93.2%.
The decline in results for the separate sciences is partly down to bright students switching to IGCSE courses and an increase in the number of 15-year-olds, who tend to perform less well, taking the exams early, JCQ said.
It added that a general trend of more students opting for the three sciences, some of whom will have lower abilities in the subject, may also have had an effect.
The results also show a "dramatic" rise in the number of entries for modern foreign languages. French entries are up 15.5%, German up 9.4% and Spanish up 25.8%.
This could be down to the introduction of the Government's English Baccalaureate, which is awarded to pupils who score at least a C at GCSE in English, maths, science, history or geography, and a foreign language.
The figures show that the overall A*-G pass rate also fell slightly this year, to 98.8% compared to 99% last year.
JCQ director Michael Turner said: "There are many underlying factors affecting this year's GCSEs, including a sizeable increase in entry by 15-year-olds, new science specifications designed with greater challenge, early and multiple entry in mathematics and an increase in the number of students taking IGCSEs. All of these have had an impact on entries and results.
"This year's upturn in languages will be welcomed across the education sector and beyond. Not since 2008 have there been this many entries in languages. However, it remains to be seen if this is the start of a trend and if more students decide to continue to study a language at A-level."
As the results were published, some schools were already reporting record grades.
King's College School in Wimbledon, a private boys' school, said 96% of its entries had scored an A* or A, with 35 pupils each gaining 12 or more A* grades in their GCSEs and IGCSEs.
At Wellington College in Berkshire, half of results were at A*, with 82% of entries gaining an A* or A grade.
The Oasis Academy chain said that on average its schools had seen a 23 percentage point improvement on their predecessor schools in the numbers of pupils achieving five or more A*-C grades, including English and maths.