Professor Alan Smithers, director of the Centre for Education and Employment Research at Manchester University, said the pass rate for the qualification aimed at bridging the gap between education and the world of work was "appalling".
He said that only 103,000 of the 260,000 students who had started GNVQs since 1992 had achieved even a partial award.
But Martin Cross, chairman of the Joint Council of National Vocational Awarding Bodies, countered: "It is important for critics to actually look at the figures and not to use emotive phrases such as 'drop out' which are not substantiated by the facts.
"Everyone wants to see higher standards of performance achieved in shorter periods of time and the evidence so far in the short life of GNVQs is that progress is being made in that direction. It would be unfortunate if too much attention were paid to one or two critics who cannot be convinced by the facts."
Their disagreement pivots on an interpretation of the total number of GNVQ results since 1992.
The Joint Council issued figures this week covering 1992-1995. But, unlike A-levels and GCSEs, they are not actually results but rather a snapshot of what has been achieved as the number of GNVQ completions changes daily.
To gain GNVQs, students must complete mandatory vocational units, core skills units and select from a range of optional units. They are awarded at foundation, intermediate and advanced level.
According to the Joint Council, a record number of students have gained full GNVQs. It claimed that since their inception in 1992, 61,604 students had achieved full awards and 41,378 had gained units towards the full GNVQ.
This year there were 217 distinctions out of 2,921 completions at foundation level; 3,493 distinctions out of 29,931 completions at intermediate and 2,858 distinctions out of 11,929 completions at advanced level. Significant numbers of students, however, did not start the foundation level GNVQ until September 1994.
Schools and colleges also do not have to report completed GNVQs on a set date, and often apply for certificates when it suits their administration arrangements.
Mr Cross said: "Everybody is rather surprised at the low percentage for whom certificate requests are made. We have no information that they dropped out. We have no evidence that they failed in any significant numbers. The Department for Education and Employment ought to do some research. It may be that the foundation is being used with special needs groups and they are taking more than a year. It is a bit of a mystery."
He said that at intermediate level 70 per cent of students who registered in 1993-94 had achievements - an increase of 30 per cent over last year. But Mr Cross said some schools and colleges had not requested any certificates yet as students often planned to go on to the advanced level.
At advanced level, of the 28,000 students who registered in 1993-94, 38 per cent (11,000) gained the full award and 25 per cent (7,500) gained the partial qualification.
GNVQ students were this week congratulated by education and employment minister Lord Henley, Labour education spokesman David Blunkett and Association of Teachers and Lecturers' general secretary Peter Smith.
But Professor Smithers, a critic of GNVQ, said that since the qualification began only 15 per cent of students had completed foundation level, a further 13 per cent achieved at least one unit but 72 per cent of registered students had nothing.
At intermediate level, 36 per cent completed, a further 11 per cent had achieved at least one unit while 53 per cent had achieved nothing. And at advanced level, Professor Smithers said, 31 per cent completed, 44 per cent had completed one unit or more but a quarter had nothing.
Professor Smithers said students wanted credible vocational qualifications but GNVQs did not offer good, applied education in their present form, and he suspected a lot of young people realised this.
He criticised the GNVQ for being "idiosyncratic", for having "a dog's breakfast of assessment" and for the multiple choice questions which surprised students because there was no syllabus.
Sir Ron Dearing is considering reform of the GNVQ as part of his review of 16-19 qualifications. Reviews of quality assessment and grading are already in progress.