Diplomas, the new secondary-level qualifications being launched by the government, are at risk of becoming the "poor relation", warns a report.
The report warns that diplomas will be second-best to A-levels
The warning comes in a review of the diplomas written by academics from the University of Oxford and the University of London's Institute of Education.
"As long as A-levels remain unreformed," the diploma will be seen as second-best, says the review.
And it warns that the timetable for launching diplomas is "unrealistic".
Diplomas, set to be introduced in secondary schools and colleges in England next year alongside A-levels and GCSEs, are intended to bridge the divide between vocational and academic qualifications.
'Qualification of choice'
The Schools Secretary Ed Balls recently predicted that diplomas could become the "qualification of choice", rather than A-levels or GCSEs.
But the review of the diploma plans, published by the Oxford-based Nuffield Review of 14-19 Education and Training, presents a less optimistic picture.
It predicts that the new qualification will be seen by teachers as an exam for the less-academically able - "with A-levels and GCSEs remaining as the more prestigious qualifications".
The report also challenges the government to be clearer about whether the new diploma structure will include A-levels.
The government recently announced that diplomas would also offer more academic subjects - making them an alternative to A-levels and GCSEs.
But the report says that this adds to the confused identity of the diploma - between academic, vocational or a "more general education purpose".
There are also strong warnings that the introduction of diplomas is too rushed.
A major concern for teachers is the "unrealistic timetable and the insufficient attention to professional development".
The review team has been led by Professor Richard Pring from the University of Oxford Department of Education and Dr Ann Hodgson and Dr Ken Spours from the Institute of Education.
A spokesperson for the Department for Children, Schools and Families said that it was not up to the government to determine the future of A-levels and GCSEs, it would be decided by "young people, schools and colleges".
The Shadow Schools Minister Nick Gibb accused the government of making a "huge mistake" in launching academic diplomas in "direct competition" with A-levels and GCSEs.