Headteachers, parents and pupils plan to fight proposals to axe eight sixth forms in south Wales. However, there is wider support for the closures in Blaenau Gwent, where the local authority has been planning a learning campus for several years.
Post-16 funding agency ELWa has come up with the plans to replace the sixth forms with central colleges offering a mix of academic and vocational qualifications. But the idea has attracted fierce criticism in Merthyr Tydfil from three of the area's four schools with sixth forms.
ELWa wants to broaden choice for teenagers and keep more of them in education after 16 as part of the Assembly's 14-19 learning pathways programme.
But Mike Johns, head of Afon Taf high school in Merthyr Tydfil, said the move would have the reverse effect and restrict choice.
He said: "We issued a questionnaire to pupils, and 90 per cent indicated they would not prefer a tertiary college. The fundamental issue is the removal of the choice of a sixth-form education for these pupils and their parents."
Alan Pritchard, head of Cyfarthfa high school in Merthyr, said parents, teachers and pupils were united in their opposition.
"There is overwhelming support for retaining sixth forms. Three of the heads believe consortium arrangements can be developed to widen opportunities."
Standing alone in his support for the plans was John Williams, head of Pen y Dre high school, who claimed the tertiary option would provide the best opportunity for all youngsters in Merthyr.
Earlier this year, ELWa launched a public consultation in the pilot areas of Rhondda Cynon Taf, Merthyr Tydfil, Blaenau Gwent, Haverfordwest in Pembrokeshire and the Dyfi Valley, Powys. Options under discussion in all five pilots included closer collaboration between learning providers, formal partnerships - that could mean joint curricula, timetables and staff - or the replacement of sixth forms with a central institution.
In the Dyfi Valley, chosen as a potential blueprint for rural areas, the preferred option is a central learning centre based at Ysgol Bro Ddyfi, which would preserve its sixth form, and is supported by head Lis Puw. In Rhondda Cynon Taf, the largest of the four areas with 19 school sixth forms, ELWa says stronger, binding partnerships between education providers would be most appropriate.
Geraint Davis, secretary of teachers' union the NASUWT Cymru, contested the proposals in Merthyr and Blaenau Gwent and called for a re-think.
"These proposals have not been properly discussed with all stakeholders and interested parties. As far as we can see none of the options have been explained properly to the teachers affected."
Gareth Jones, an executive member of the Association of School and College Lecturers Cymru, said: "There's an assumption that tertiary is the best option, which has not been proven."
A spokesman for ELWa said every effort had been made to raise awareness of the proposals.
He added: "Should a need for substantial changes be identified in any pathfinder area, more consultation with learners and parents will be necessary before a final decision can be made."