Vocational GCSEs, which thousands of students are expected to sit, are due to be introduced in September 2002 as part of the Government's bid to expand work-related learning.
They will replace general national vocational qualifications and are graded A to G to align them with academic GCSEs. About 200,000 GNVQ exams were sat this summer.
Vocational GCSEs will be available in eight subjects including manufacturing, engineering and health and social care and will be the equivalent of two GCSEs. External exams will count for a third of marks.
Ministers believe it is "essential" that the new GCSEs be launched next year and have ignored Qualifications and Curriculum Authority advice to delay until September 2003.
The new GCSEs are expected to simplify the qualifications system. Their courses will be more rigorously assessed and it is hoped they will have equal status with academic GCSEs.
But the speed of change has led to fears that their introduction will lead to similar difficulties to those that dogged vocational A-levels which replaced advanced GNVQs last September.
The problems posed by the new A-level were highlighted by the QCA inquiry into the post-16 reform chaos, ordered by Education Secretary Estelle Morris.
Its report highlighted concerns that the vocational A-level was pitched too high - more than three-quarters of students failed exams last January in some key subjects. The QCA also doubted whether vocational subjects should be examined in the same way as academic ones.
Professor David Hargreaves, QCA chief executive, will produce his full report on vocational A-levels in December. But his conclusions will be too late to inform vocational GCSE syllabuses, scheduled to be published in the New Year.
John Dunford, general secretary of the Secondary Heads Association, said:
"It is bizarre that, given the furore this summer, the Government is forcing through vocational GCSEs."
Former assistant chief executive of the QCA Tony Millns criticised the rush to impose new qualifications without questioning how they would work in schools. He said the Government originally planned AS-level changes for this year - not 2000.
Professor Hargreaves expressed reservations about the speed of change as he launched the AS inquiry: "We are surely learning that untested and untrialled innovations can destabilise and confuse," he said.