By Gary Eason
BBC News, at the NUT conference
Children may leave school with vocational Diplomas recognised only by school sponsors, teachers have warned.
Teachers are concerned about the credibility of vocational Diplomas
The National Union of Teachers conference has voted to oppose the introduction of the new qualifications.
It said the Diplomas - being introduced in England from next year - would go hand in hand with academies sponsored by employers seeking cheaper labour.
The government says Diplomas are one of the most significant educational reforms in many years.
The NUT conference, in Harrogate, also heard calls for secondary schools to close for an extra two days' teacher training so they could prepare for the "overload" of new initiatives in 2008.
As well as the Diplomas these include a revised curriculum, new GCSEs and A-level changes.
The specialised Diplomas are being designed to involve a mix of practical and theoretical learning in a range of employment sectors.
The first five are due to start next year, in 145 pilot areas involving some 40,000 young people.
Education Secretary Alan Johnson himself has said the Diplomas could go "horribly wrong" if they are seen as second best.
The NUT conference said the Diplomas "continue to exhibit the weaknesses of existing vocational qualifications" and the union should campaign against their implementation.
A spokesperson for the Department for Education and Skills said: "It's pure nonsense to suggest that diplomas will do anything other than give young people the chance to fufil their potential. "Diplomas will provide the missing link - creating the mix of vocational and academic education which we've lacked for so long and form a key part of our plans to encourage more to stay until 18."
A London teacher, Michael Davern from Southwark, said young people were being given just enough education to perform one job for the rest of their lives.
In Manchester, academies were being set up to produce workers for the sponsors' firms, he said.
"Imagine leaving school at 16 with a Diploma that is recognised only by the factory up the road."
Coventry teacher Glen Mynott said teenagers would have a very narrow curriculum if they opted to pursue a Diploma.
"What will be the employment options for a youngster with a Diploma in hair and beauty?" he said.
Martin Allen, from Ealing in London, said the expectation now was that people would change jobs many times during their careers.
"Why would anyone want to do a specialised Diploma for four or five years?" he said. "I wouldn't."
The government has said it wants people to be in education or training to the age of 18.
The conference resolution recognised the importance of high quality school or college education for those aged 16 to 18.
But it said that unless work-based training was sufficiently well resourced, and properly rewarded, "young people will be exploited by businesses and used as even cheaper labour".
It called for an independent review of vocational education involving the education unions, researchers, employers' representatives and youth organisations.