The end of GCSE grade inflation will lead to a sharp plunge in results in two years' time because of changes to the way the exams are sat, an academic study has predicted.
This summer the proportion of A*-C GCSE grades fell by 0.4 per cent, the first decrease in the qualification's 24-year history.
A paper from King's College London concludes that the switch demanded by ministers from modular to linear exams in 2013-14 is likely to lead to a much steeper drop. It quotes research on previous exams, which suggests that the proportion of pupils achieving C grades in GCSE English will fall by between 3 and 7.5 percentage points.
GCSE English is already at the centre of an ongoing controversy this year after Ofqual's "comparable outcomes" efforts to combat grade inflation resulted in the regulator demanding that exam boards overrule their examiners' judgements to prevent results from climbing.
Overall A*-C GCSE English grades fell by 1.5 percentage points this June. But that masked hundreds of schools experiencing unexpected drops of between 10 and 20 percentage points compared with 2011.
Laurie Smith, a King's College London education lecturer and former senior examiner, said Ofqual will not have to use comparable outcomes to combat grade inflation in 2014. His paper states that the move to linear, end-of-course exams will do the job without the regulator having to act.
"Unless schools develop different teaching approaches, the discontinuation of modular GCSE English is likely to result in a considerably greater reduction of GCSE English A*-C grades than in 2012," he writes.
Mr Smith cites a Cambridge Assessment study that analysed the performance of all candidates sitting an OCR English GCSE between 2004 and 2009. The qualification had five modules. They could either be taken together in a linear fashion at the end of a course, or in a modular fashion at different stages during the course - with one resit allowed per module.
The final grades of candidates opting for the two routes were compared. Over the six years, modular candidates exceeded linear candidates at grade C by an average of 7.5 percentage points in half of the exam sessions, Mr Smith writes. In the other half the difference found at grade C was negligible.
The Cambridge Assessment research also found that modular candidates' option to resit modules increased the proportion of grade Cs by an average of 3 percentage points.
"On the evidence of this research, the discontinuation of modular GCSE English appears likely to result in a reduction in 2014 of between 3 and 7.5 (percentage points) at grade C," Mr Smith concludes.
But Brian Lightman, general secretary of the Association of School and College Leaders, said: "I don't see any reason to expect that. There should be proper grade criteria that decide what the quality of work is at a certain standard. If you have that then the timing of an exam shouldn't matter.
"A lot of this debate has turned into one about statistics and accountability, rather than focusing on standards."
Mr Smith's paper speculates about whether Ofqual will step in to prevent a sharp drop in results triggered by the end of modularity. He argues that the regulator is "unlikely" to do so because of its public commitment to combating grade inflation.
An Ofqual spokeswoman said: "We will be discussing how we approach the first fully linear awards in due course."
To read the study, Maintaining and Improving GCSE English Grades in Linear Examinations, go to bit.lyS5Mjfg.