Independent schools are more likely to challenge exam results and be successful in their requests for reviews of marking than the vast majority of state schools.
Heads leaders are warning that this means that pupils in state schools, already hit by real terms school funding cuts, are being "doubly disadvantaged".
At both GCSE and A-level, independent schools put in more challenges to exam boards than state schools, according to an analysis of the latest figures from the exams regulator, Ofqual.
Independent schools requested reviews for 8.1 per cent of their GCSE entries – which is more than academies (5.5 per cent) and other comprehensives (5.6 per cent), the 2016 figures show.
And the analysis reveals that 20.9 per cent of GCSE grades challenged by independent schools were changed, compared to 17.3 per cent for comprehensives and 17.5 per cent for academies.
However that rate of successful challenge is matched by one small group of state schools: grammars – although these selective secondaries requested a smaller proportion of reviews of GCSE results than theindependentt sector - at 6.2 per cent.
Geoff Barton, Association of School and College Leaders general secretary, suggested the difference in appeal rates between the sectors could be explained by state school budgetary pressures.
"It might be that independent schools are able to put more money into [re-marks]," he said. "If so, that does raise quite big questions ss it could be that children in schools with lower budgets are being doubly disadvantaged.
“It certainly isn’t because the state sector teachers don’t care. They will be just as concerned."
However, independent schools do not necessarily have the highest percentage of grades successfully challenged when the figures are broken down across individual subjects.
The Ofqual figures – which look at 13 GCSE subjects and nine A-level subjects - show that independent schools only have the highest percentage of GCSE grades changed relative to grades challenged in five subjects: English, English literature, physics, science and geography.
Academies have the highest percentage of grades changed relative to grades challenged in biology and additional science; colleges in chemistry; and grammar schools in maths, history, French, German and Spanish.
Today pupils will receive their GCSE results – and in England, teenagers will receive numerical grades 9-1 in English and maths for the first time, alongside A* to G grades in their other subjects.
Mr Barton thinks it is likely that more schools will request remarks in light of the reformed GCSEs, echoing teachers' warnings previously reported by Tes.
"One of the reasons for that is because it is now pretty much all reliant on the final exam – as opposed to coursework or controlled assessment – it means that what you haven’t got is some initial indicator as to how that student might do," he said.
"Now for a lot of people in schools in the first year of the exam, their heads are spinning as they do not know at all what that child might get. So I think that is likely to lead – in the first year of an exam – to far more requests for remarks because of the level of uncertainty.”
The Ofqual figures show that independent schools requested reviews for 9.8 per cent of their A-level entries – which is more than comprehensives (4.7 per cent), academies (6.2 per cent) and grammars (5.5 per cent).
It also reveals that 17.5 per cent of A-level grades challenged by independent schools were changed - compared to14.5 per cent for comprehensives, 15.5 per cent for academies and 14.8 per cent for grammars.
Mary Bousted, general secretary of the Association of Teachers and Lecturers (ATL), said: “I think [independent schools] are more likely to challenge because they have got more resources to do so.
“In particular, parents who are prepared to pay the fees to challenge and state schools have less available to cash to do that. And I suppose the more you challenge the more successful you are going to be.”