Despite near-consensus among maths teachers of the need to reform the GCSE, it will not be changed until 2008, the Qualifications and Curriculum Authority has confirmed.
The authority says it is taking its time over changes to the qualification because of previous rushed reforms such as the Curriculum 2000 relaunch of A-levels.
However, John Dunford, general secretary of the Secondary Heads Association, said he could not see why schools could not start teaching for the new GCSE next year, with pupils sitting the new exam in 2007.
Professor Adrian Smith's recent report on maths teaching reserved some of its fiercest criticism for the structure of the GCSE exam, taken by 713,000 pupils last year and divided into three tiers.
The higher tier is taken by students aiming at grade C and above and intermediate by those expecting grades E to B. The foundation tier, available to those aiming for a grade D, is taken by around 30 per cent of pupils.
Professor Smith said it was unacceptable for foundation candidates to be given no chance of a grade C: many felt like failures even when starting courses at 14.
The QCA agreed so strongly with Professor Smith that it proposed in its evidence to introduce a new two-tier GCSE where all students would have a chance of a C this year. It said that teaching of the award could begin in September, with the first exams in 2006, two years earlier than the Government's original proposal.
The QCA evidence said that students achieving a grade B through the intermediate route were unlikely to have met some of the key ideas needed for A-levels. The three-tier structure demotivated less academic pupils, it added.
The two-tier exam was piloted in a few schools last summer. The QCA evidence suggested abandoning a second pilot to speed up the new exam's national introduction. But now the QCA has reverted to its original timetable.
A spokesman said: "There was a suggestion that it might have been possible to have only one year's pilot.
"But we have encountered problems in recent years when new exams have been rushed in. No one wants, especially in a subject such as maths, to have changes that are rushed."
The TES understands that exam boards were sceptical about the 2006 start date. It is possible that repeated delays in the publication of Professor Smith's report - originally scheduled for last June - may also have influenced the timetable.
In other evidence to the inquiry, England's largest exams board admits higher and intermediate students can gain a grade C with little mathematical knowledge.
The AQA board says: "Average students may gain a grade C but possess only discrete lumps of mathematical knowledge with little idea of how they fit together or how maths skills can be applied."
The board also said children's education may be suffering from the emphasis, at key stage 4, on passing GCSE exams.