Ministers are wrong to believe the English Baccalaureate can be achieved by all and need to come up with alternatives for pupils of different abilities, according to a think-tank.
Matt Grist, senior researcher at Demos, says the EBac - which requires GCSEs or IGCSEs of at least grade C in English, maths, a humanity, a language and two sciences - is only ever likely to be achieved by a minority of pupils.
"The EBac is so hard I can't see it going above 35 per cent (of pupils achieving it), except maybe in large areas of upper middle-class kids," he told The TES.
"The EBac is for bright kids who are going to be academic, so we need other well-designed curricula for kids in other streams."
Just 15.6 per cent of pupils achieved an EBac last year. But that figure was based on GCSEs sat before schools were told they were to be judged on the measure.
Ministers believe that in future all pupils should have an EBac. But Dr Grist thinks that policy could lead to less academically able children missing out.
He sees the development of the EBac as an ideal opportunity to open up alternative routes for 14-year-olds and will make his case on Tuesday at a Cambridge Assessment seminar called "Is 14 the new 16?".
He agrees with another speaker - Cambridge Assessment's research director Tim Oates - that a desire to achieve "parity of esteem" between academic and vocational qualifications has previously damaged the education of pupils who need it most.
Now Dr Grist believes they could be about to suffer again.
"We haven't put enough thought into different curricula for pupils of all abilities and different kinds of abilities," he said. "It is the pupils at the bottom end of the range that tend to miss out because of that."
Sir Michael Wilshaw, one of the Government's favourite heads, shares some of these concerns.
In February, the headteacher of Mossbourne Academy in Hackney, east London, publicly asked the Government to include a "technical and craft-based curriculum option" in its national curriculum review.
He said there would always be pupils "for whom an academic curriculum is not appropriate".
Watch the seminar live at www.cambridgeassessment.org.uk.