The number of secondary schools considered to be under-performing has doubled to more than 300 in the wake of a major overhaul of the exams system, official figures show.
The statistics, released today, show 330 state schools fell beneath the government's floor target this year after failing to ensure that enough pupils gained five good GCSE grades and made sufficient progress, according to an analysis of new league tables.
The Department for Education (DfE) insisted that the rise is down to two key reforms - a decision that only a teenager's first attempt at a GCSE would count in the annual performance tables, and a move to strip poor quality vocational qualifications out of the rankings.
Dozens of schools, the vast majority of them in the independent sector, have seen their results plummet to zero because some combinations of English GCSEs and some IGCSEs do not count in the rankings this year.
The increase in schools falling beneath the floor target is likely to cause concerns among school leaders, who have voiced fears that schools will be considered failing not just due to changes in the system but also"volatility" in last summer's GCSE results.
State secondaries are considered to be under-performing if fewer than 40 per cent of their pupils gain at least five C grades at GCSE, including English and maths, and students are not making good enough progress in these two core subjects.
In total, 330 schools fell below the benchmark this year, up from 154 last year, the government's figures show. Schools that fall below the threshold could face action, including being closed down and turned into an academy, or being taken over by a new sponsor.
However the DfE insisted that the floor standard is one of a number of factors that schools are judged on and falling below the benchmark does not automatically mean that a school will face intervention.
It also said that the two major changes to the exams system - which schools were told about around 18 months ago - do not affect pupils individual exam results.
Ofsted, too, said that while exam results are looked at when it decides which schools to inspect, falling below the floor targets would not automatically trigger a visit from inspectors.
“Ofsted takes a number of factors into account when conducting a risk assessment, one of which will be the academic achievement of pupils over time, taking into account both their attainment and progress," a spokesman added.
Education secretary Nicky Morgan said: "For too long pupils were offered courses of no value to them and schools felt pressured to enter young people for exams before they were ready.
"By stripping out thousands of poor quality qualifications and removing resits from tables some schools have seen changes in their standings.
"But fundamentally young people's achievement matters more than being able to trumpet ever higher grades. Now pupils are spending more time in the classroom, not constantly sitting exams, and 90,000 more children are taking core academic subjects that will help them succeed in work and further study."
Ms Morgan added that the government has "raised the bar" and that schools are already rising to the challenge.
Earlier this week the Association of School and College Leaders (ASCL) claimed that the government floor targets are "pretty much irrelevant" this year due to the upheaval in the exams system.
ASCL general secretary Brian Lightman warned against judging the nation's schools on one set of exam results, saying too much has changed compared with 2013 to draw accurate comparisons from year to year.
Last summer's GCSE results showed a sharp drop in English grades, with 61.7 per cent of entries scoring A*-C, down 1.9 percentage points from last summer. This is believed to be the biggest drop in the qualification's history. Maths saw an opposite result, with 62.4 per cent of entries gaining an A*-C grade, up 4.8 percentage points on 2013.
An analysis of the data indicates that the most improved school was the Charter Academy in Southsea which saw has seen its results rise from 39 per cent of students getting at least five Cs including English and maths in 2011 to 83 per cent achieving this standard in 2014.
This year's top school for GCSEs was King Edward VI Five Ways School, an academy in Birmingham. It entered 155 pupils for GCSEs and equivalent qualifications and all scored at least five C grades, including English and maths. It also had the highest average points score per pupil at 685.5.
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