The future of further education is raising concerns, especially in the south Wales valleys, a BBC Wales investigation has found.
It follows a decision by the assembly government to ask all local authorities to review post-16 education.
But measures that could see school sixth forms closed altogether in some areas has sparked an angry reaction.
The Eye on Wales programme, broadcast on Monday, found that in one case plans could face a lengthy legal fight.
It comes as protests took place last week by school pupils in Merthyr Tydfil as their council took the next step towards radically re-organising their education once they reach 16.
Their council is just one of a number across Wales proposing new colleges dedicated to delivering education and training after GCSE.
The move followed a request by the Welsh Assembly Government to ask all 22 local authorities to come forward with plans to deliver a wider variety of both traditional academic and more practical vocational courses from the age of 16 in a bid to increase student numbers.
According to David Egan, professor of education at Uwic, Cardiff, most councils are proposing improved collaboration between existing sixth forms and further education colleges.
But five councils, including Blaenau Gwent, Torfaen and Rhondda Cynon Taff, as well as Merthyr Tydfil, are looking at more far-reaching proposals.
"Clearly there are issues about demography in the Valleys which are considerable issues and are obviously such that it's understandable that radical solutions are now being looked at," said Prof Egan.
One such solution is on offer at The Works in Ebbw Vale, the massive 200-acre site that has been reclaimed for development following the closure of the town's steelworks in 2002.
Part of Blaenau Gwent council's vision for the site involves new primary and secondary schools for the town and a new, post-16 institution serving the whole of local authority.
"Everywhere in Wales we have a falling birth rate and we have lower numbers of young people in education. If we don't do something we're going to have schools that are in real problems with viability of their sixth forms," said Steve Bard, Blaenau Gwent's executive member for education.
"The exciting project we have now is a way of bringing students together.
"The larger the pool of students we have, the wider choice you can offer, the more courses will become financially and educationally viable.
"This is a real opportunity to have a larger unit in purpose-built facilities, really wide set of options to as many students as possible.
"We believe that we can provide a really strong education, real futures for the young people here in Blaenau Gwent."
But to achieve the council's vision the four sixth form departments in the borough would have to close.
The largest, with some 230 pupils, lies just a few miles from The Works at Brynmawr Foundation School.
Head teacher James Retallick told Eye on Wales that he views that prospect with some concern.
"If you were to ask any of the parents they would be very disappointed if this school lost its sixth form," he told the programme.
"Part of their choice is around the fact that we have a sixth form and they feel that there is a good continuum of education through from one of the school at Year Seven all the way up to when they leave the school in Year 13."
"That does form part of the school's character.
"For example we do operate a buddy scheme, a lot of our sixth formers are helpers in our youth club.
"That is the type of provision that would not be available in a further education setting."
Brynmawr's concern is that the current proposals are for the new institution to be run by the local FE provider, Coleg Gwent.
Brynmawr's answer is to run the enterprise itself or together with other local schools.
Blaenau Gwent is currently considering those ideas.
But what happens next could hinge on legal interpretations of Brynmawr's unusual status as a foundation school, which puts it outside of direct council control.
The chairman of Brynmawr's governors, Coun Lyn Elias believes that, as the law stands, the council and the assembly government do not have the powers to impose the closure of its sixth-form.
"Primary legislation at this moment in time has not been handed down to the Welsh assembly," he said.
"It would have to go through a process of an assembly measure or legislative competence order.
"We have taken advice from a top-class solicitor in education and a QC and at this moment of time we are on the right side of the law. It could possibly go to a judicial review."
"We're concerned about the standard of education that's going to be in the new building in Ebbw Vale and who provides that standard of education. We only want the best."
Blaenau Gwent council argues that its plans will provide the best for the most and that it does have the powers to realise its vision. It hopes to put out proposals for formal consultation in the coming weeks.
Eye on Wales is on BBC Radio Wales at 1830 GMT on Monday 25 January. You can listen on 93-104 FM, 657 & 882 MW or on digital satellite: Sky - 0117 or Freesat - 714, Freeview on 719 or cable 931.