A conservative government would scrap measures used to demonstrate the achievements of schools with tougher intakes as part of a huge overhaul of the exam and league table system, it emerged this week.
Contextual value added (CVA), used in league tables since 2006, has been welcomed by schools serving "challenging" areas because it takes factors such as pupil deprivation into account when comparing the value schools add through exam results.
But the Tory-commissioned review of the English exams system, conducted by Sir Richard Sykes and published this week, attacks the "implied precision" of CVA as "spurious", which it says makes the measure "unfair" to schools, teachers, pupils and parents.
The review says it should be abandoned, along with value added, unless the "underlying validity to their methodology" can be proved. A leading academic said this week that it could take five years to develop a replacement measure.
But Michael Gove, shadow schools secretary, said he thought CVA should go. "I believe the current measures are flawed and there is an ongoing debate about how to improve on it," he said. "My view is that they make comparisons on the basis of assessment techniques which are themselves flawed. We need to take several steps back and work out how to reconstruct measures that are more appropriate."
The prospect of it disappearing follows the decision by Ofsted to place much more emphasis on raw exam results in its increasingly data-driven judgments on schools.
But John Dunford, Association of School and College Leaders general secretary, said it currently stood as the fairest measure available.
"CVA may not be perfect but it's a fairer measure of performance than value added, and value added is fairer than raw results," he said.
"We would work with a potential Conservative government on how to improve CVA or to ensure a similar measure is created that recognises the context in which a school sits."
Professor Stephen Gorard, from Birmingham University, has warned about the dangers of the measure before it was even introduced. He said there was so much missing data and "measurement error" that the end result was a "nonsense".
"If the use of CVA continues I think there will come a time when it results in court a case," he said.
Professor Gorard added that the measure had been rushed in before being properly evaluated. There were potential alternatives, but they could take five years to develop before being ready for publication.
Mick Brookes, general secretary of heads' union the NAHT, backed the idea behind CVA but admitted that it had become "too complicated".
"We have to find a way to recognise those schools which have the most challenging children and celebrate what they are doing in order to build up confidence," Mr Brookes said.