The country's leading colleges are calling for a cull of "inefficient" small school sixth forms.
The 157 Group says cutting provision by small sixth forms would offer increased value for money and boost the quality of education on offer.
A policy paper by the group says large colleges are able to deliver economies of scale, educational opportunities and facilities beyond the reach of small sixth forms.
"Small sixth-form groups are viable only if they severely restrict the range of courses on offer; larger institutions can combine financial viability with real choice," it says.
"The proliferation of small sixth forms therefore risks undermining the quality of education and students' ability to choose."
It says research shows that the unit cost of a cohort of 100 students can be twice as high as for a cohort of 500. It cites evidence that the average A-level points score achieved in sixth forms rises as pupil numbers increase.
The group says a more efficient model for delivering qualifications, like the 14-19 Diplomas, involves colleges acting as hubs that provide resources to a range of schools and sixth-form "spokes" through partnership arrangements.
"The advantages of the `hub-and-spoke' model are most apparent when considering the investment in workshops," the paper says. "A college location maximises the opportunity to share expensive facilities between young people and adult programmes, and to share the cost of well-qualified technician staff."
It argues that colleges would provide greater educational choice for young people who are often faced with an eitheror choice between academic or vocational routes.
The report also criticises Diplomas, saying that while they play a part in extending choice, they are insufficiently vocational for pupils with a more practical bent. The group warns against replacing existing vocational courses such as Btecs or City and Guilds with Diplomas.
While the group supports the government changes whereby responsibility for commissioning 14-19 education will be handed to local authorities on April 1, there are concerns this will not give colleges the freedom to deliver truly demand-led education and training.
The paper says: "There are worrying signs that some may see the role as another opportunity to engage in labour-market planning. In a fast- changing world, the information on which the planners work is inevitably out of date."
Colleges are also worried about local authorities' understanding of the further education sector.
"It is vital that this potential `awareness gap' is bridged as quickly as possible to ensure the potential contribution of colleges is maximised and not accidentally curtailed as a result of limited knowledge." the paper says.
The Association of School and College Leaders (ASCL), which has members in schools with small sixth forms and in larger colleges, said the call to cut "inefficient" sixth forms was unhelpful.
Martin Ward, assistant general secretary at the ASCL, said: "As far as possible, we should allow students to make their own choices, and for some that will be a small sixth form.
"Although that does not mean we should be subsidising some providers, the argument that we should shut down small providers rather cuts against that choice."
David Igoe, chief executive of the Sixth Form Colleges' Forum, said: "Our position is not a million miles from that of the 157 Group. But I think sixth-form colleges would take issue with any argument that said that the hub-and-spoke model is the most efficient way to deliver 14-19 education.
"There is a danger that big colleges become the sole, monolithic providers in an area, and if that doesn't suit a particular student, then too bad."