The "credibility" of the Government's 14-19 diplomas has been questioned by a committee of MPs.
A proper understanding and acceptance of diplomas as an entry qualification by higher education institutions is "some way off", MPs on the Commons Public Accounts Committee warned.
The diplomas have been hailed by ministers as a potential replacement for GCSEs and A levels. The first tranche were introduced last month, with the aim that all 14 new qualifications would be available to all pupils in England by 2013.
But the committee says in Preparing to Deliver the 14-19 Education Reforms in England: "There is still much work to be done to convince parents, employers and universities that diplomas are a credible alternative to existing qualifications."
It also warns that diplomas could "further complicate an already complex system of qualifications".
Schools Minister Jim Knight said: "Working with our partners in local authorities, schools and colleges, we recognise there is more work to be done to provide students with the quality and flexibility of learning that employers and universities today want."
- Universities' efforts to widen participation may have got more people into higher education, but they have failed to make the system fairer, according to new research.
Unveiling the preliminary research results at a seminar organised by the Helena Kennedy Foundation, Miriam David, professor of sociology of education at the Institute of Education, said that inequalities persisted in the system.
Her work, funded by the Economic and Social Research Council, demonstrated that middle-class students were more likely to study at the "elite" universities while non-traditional students from less well-off backgrounds were more likely to study at a post-1992 institution.
"Inequalities are sustained in terms of the institutions (attended)," she said. "Despite the increase in opportunities and the diversity in higher education, who goes where is still a question. Although people have more educational opportunities than in the past, they don't have equal educational opportunities."