The new Vocational A-level qualification is not popular with learners and was not well designed, England's school inspectorate has said.
Ministers say Vocational A-levels are being redeveloped
Ofsted said the qualifications were "neither seriously vocational nor consistently advanced".
In a report on their first two years of operation, it said there was more unsatisfactory teaching than in 16 to 19 education generally.
In response, the Qualifications and Curriculum Authority (QCA) exams regulator has said the new A-levels are breaking down the "damaging divide" between academic and vocational qualifications.
Vocational A-levels replaced the Advanced GNVQ as part of the Curriculum 2000 reforms.
But Ofsted said their aims were not clearly understood by many teachers and students.
The inspectors arrived at their conclusions after making 78 visits to a sample of 45 colleges and nine secondary schools during 2002 and 2003.
In some subjects, course specifications lacked vocational content and were too similar to A-levels, they said.
"The assessment regime is regarded by Ofsted, teachers and students as excessively complex and bureaucratic.
"Teachers still spend too much of their time assessing, rather than teaching, and students spend too much time completing assessments rather than learning.
"There is a lack of consistency in the grades awarded to students for work of a similar standard."
Colleges - where most Vocational A-levels are taught - endorsed Ofsted's comments and said they had been telling the government about the problem for some years.
Judith Norrington, Director of Curriculum and Quality at the Association of Colleges, said colleges had to be very careful in advising young people about taking these qualifications.
"While they are suitable for those wanting to study vocational subjects in a largely academic or theoretical way, they do not offer the full range of engagement with the practical aspects of vocational learning which many young people want."
She added: "Because of these concerns, there has been a noticeable swing in college provision back to traditional vocational qualifications such as BTecs."
Ofsted's chief inspector, David Bell, said the report was "worrying".
Action should now be taken to increase the vocational skills component and make work experience mandatory.
The QCA should review the specifications of the courses, he said.
The QCA's chief executive, Ken Boston, said changes to the qualifications were being introduced next year.
"They will continue to provide a broad introduction to a vocational area and will encourage distinctive teaching and assessment approaches in a work-related context.
"These are innovative and dynamic qualifications which have helped to reduce the damaging and artificial divide between academic and vocational subjects." He was confident that students could be proud of them.
Head teachers agree
The Department for Education and Skills said vocational qualifications were central to the government's education reforms.
Mike Tomlinson's working group on 14-19 reform was considering the longer-term developments, which would include an improved "vocational offer".
An increase in the number taking the qualifications was expected, it said.
But head teachers also think Ofsted's criticisms are accurate.
John Dunford, the general secretary of the Secondary Heads Association, said: "They have tried to make Vocational A-levels too much like academic A-levels, particularly in relation to exams and assessment.
"What is needed is an entirely different kind of vocational course to the same standards as A-level but sufficiently different to motivate young people who are more suited to this kind of course."
Liberal Democrat education spokesman Phil Willis said young people and employers wanted high quality vocational courses that had real standing.
"If the government is serious about developing a strong vocational curriculum it needs to abandon its obsession with A-level parity of esteem.
"Close co-operation with employers is essential in providing qualifications and courses that have got real status."