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The biggest impact on this year's GCSE results have stemmed from changes that mean students did not sit exams early, compared to previous years when pupils could take GCSEs multiple times, exam chiefs suggested.
This year, only a teenager's first attempt at an exam would count in school league tables, so schools that had traditionally made use of the winter exam season, entered pupils early, or made use of resitting are likely to have seen the greatest changes.
– Michael Turner, director general of the JCQ
There has been a significant amount of change to the system this year and although UK level figures are relatively stable we expect more schools and colleges to see volatility in their results. The extent of this volatility will depend on how much change from their usual practices they experienced and how they adapted.
Entry patterns are very different this year. We have seen a dramatic decline in the number of entries from 15-year-olds, which is largely due to a change in the school accountability measure, where a candidate's first entry counts in performance tables, and the move to end-of-year exams in England.
As we would expect, where the change in entry patterns is greatest, such as the sciences, English and maths, we have seen some impact on results. But despite these changes and the potential for increased centre volatility, candidates can be confident that standards have been maintained.
Today's GCSE results show that girls once again lead pass rates at grade C and above, with 73.1% of girls' entries scoring A*-C compared with 64.3% of boys'.
However, official results showed that boys are beginning to close the gap at A*, with 5.2% of entries scoring the top grade compared with 8.1% of girls'. The difference of 2.9 percentage points is down from three percentage points last summer.
The proportion of GCSE exam students awarded at least a C grade has risen for the first time in three years, official figures show.
Just over 68.8% of exam entries scored A*-C - up 0.7 percentage points on last summer, statistics published by the Joint Council for Qualifications (JCQ) show.
In maths, 62.4% of students were awarded an A*-C grade - a significant 4.8 percentage points on last year's results.
Exam chiefs suggested that changes to this year's entries, including fewer lower-performing 15-year-olds taking the GCSE early, are behind the hike.
In contrast, 61.7% of English entries scored a C or higher, down 1.9 percentage points from last summer.
The drop - believed to be the biggest in the qualification's history - could be down to strong candidates taking advantage of the chance to sit the exam last winter, the JCQ suggested.
The proportion of entries awarded an A* - the highest grade - has dropped to 6.7% from 6.8% last year. It is the third year in a row that the number of students achieving the top pass rate has fallen.
Islamic State militants pressed for a ransom before killing journalist James Foley and are threatening to kill three other US hostages if their demands are not met, an American newspaper claims.
The New York Times, citing a representative of Foley's family and a former fellow hostage, reports that the US refused demands to pay a "multimillion-dollar ransom" for his release.
The newspaper claims that IS is also threatening to kill at least three other Americans if it does not receive ransom payments.
The report follows interviews with "recently released prisoners, family members of the victims and mediators attempting to win their freedom".
Many European nations have previously agreed to pay ransoms for hostages held by terror organisations, though Britain and the United States have continually said they will not.
Scientists believe they could have discovered 'life in space' after finding traces of sea plankton on the surface of NASA's International Space Station.
Following detailed experiments of the samples, experts confirmed organisms can live in space for a number of years despite zero gravity, harsh temperatures and hard cosmic radiation.
Vladimir Solovyev, chief of the orbital mission on Russia's ISS wing, told Russian news agency ITAR-TASS it was not quite clear how the microscopic particles appeared on the surface of the space station.
He said more research was needed but added: "The results of the experiment are absolutely unique."
More UK aid flights have departed for Iraq today, delivering tents, food and vehicles for humanitarian workers across the north of the country.
Taking off from Dubai today, the flights will deliver the supplies to refugees across the Dohuk region, who have been chased out of their homes after threats and attacks from Islamist extremists.
The first UK aid flight was on August 16, and delivered almost 8,000 kitchen sets allowing people to cook for themselves.
The contents of the latest delivery, bringing to six the total number of flights to date, are aimed at providing shelter for 2,575 people, as well as body armour for aid workers.
The area around the Bardarbunga volcano in Iceland has been evacuated over fears it could erupt.
Iceland's civil protection agency ordered the evacuation after "increased seismic activity" at the country's largest volcanic system.
A statement from the agency said: "This decision is a safety measure. It cannot be ruled out that the seismic activity in Bardarbunga could lead to a volcanic eruption."
Ash from the eruption of Iceland's Eyjafjallajokull volcano in 2010 shut down much of Europe's airspace for six days.
Prime Minister David Cameron is to return to his holiday Cornwall today but will continue to receive regular updates and briefings, Downing Street says.