GCSE changes 'could see unpredictable results'
The government's planned overhaul of GCSEs in England could see results "varying more than normal" for several years, the exams regulator has said.
The changes could result in GCSE exam results becoming less predictable, Ofqual said.
In a letter to Education Secretary Michael Gove, the head of Ofqual, Glenys Stacey, called for a period of stability in the exams system.
Her comments are in response to a consultation on school accountability.
In February, Mr Gove announced that secondary schools in England would no longer be judged on the proportion of pupils who achieved five or more A*-C grades at GCSE, including English and maths.
Instead two new league-table measures will be introduced, examining the percentage of pupils who reach a set threshold in English and maths, and an average points score showing how much progress each child makes between the end of primary school and GCSE level in eight subjects.
This followed concerns that current accountability measures encourage schools to "play the system" to boost their league-table standing.
In her response to the Department for Education's (DfE) consultation on the changes to accountability, Ms Stacey says she believes the proposals are "very much in the right direction".
But she notes that the plans mean the subjects included in the "best eight" measure are counted equally.
"You may want to consider giving different weights to the eight qualifications to recognise the particular importance of English and maths in the overall mix."
She also says league tables should not "over-emphasise" certain grade boundaries in key subjects.
"You will need to make sure you do not over-emphasise grade threshold measures of threshold performance in key qualifications."
The letter continues: "Ideally, qualifications used in accountability measures will be kept stable over a period of years.
"When qualifications change, results vary more than normal - both between schools and from year to year - and this variability is inevitable for several years as reforms work their way through the system.
"What is more, with improved GCSE assessment, results are likely to prove less predictable in future years, and more variable school by school.
"It is tempting, as soon as something is quantified, to assume it to be a more precise measure than it can ever really be.
"This needs to be recognised in the use of accountability measures by DfE, Ofsted and other users."
The government has announced plans for major GCSE reform which will see exams sat at the end of two-year courses, rather than in modules throughout, as well as an increase in extended questions and less internal assessment.
Revised GCSEs in academic subjects, including English and maths, are due to be introduced in 2015.
However, Mr Gove stopped short of introducing a new qualification for 16-year-olds called the English Baccalaureate Certificate (EBCs).
A spokeswoman for the DfE said: "Ofqual is clear that the current system is affected by perverse incentives, distorts teaching, narrows the curriculum and places too much pressure on qualifications.
"The regulator also says our proposals to develop accountability measures are in very much the right direction. We have recently consulted on proposals and will respond in due course."