The Welsh Conservatives say a return to grammar school-style education in Wales is needed to boost standards.
Under their proposals, children would be assessed at the age of 14 and encouraged to follow either academic or vocational studies.
The idea has been criticised by opponents for turning the clock back to a divisive and discredited system.
David Evans, Secretary of the National Union of Teachers (NUT) Cymru, said they back the comprehensive schools system fully.
He said "it suits us - its suits the people of Wales - it suits the children of Wales."
The last grammar school in Wales closed in 1988, but the Welsh Conservatives are calling for a return to the grammar system.
Myles Blood is 18 and from Cardiff. He is a catering trainee with ACT Training. He says he stayed in school to do his AS-levels, but wishes he had gone down the vocational route earlier.
He told our Political Editor Adrian Masters "if I started this at 14, I think I'd be a year into a job, and a professional demi-chef."
The Welsh Conservatives have proposed a streaming system in Welsh secondary schools, where pupils are separated between academic and vocational streams at age 14.
The National Association of Head Teachers (NAHT) Cymru says it is concerned that the Welsh Conservatives' proposals for a return to a grammar school system "raise more questions than they answer."
The Welsh Conservatives have proposed a return to a grammar school system in Wales, saying it would raise standards.
The party wants pupils to be separated into two streams - academic and vocational - at the age of 14.
There are no grammar schools left in Wales, but 164 in England.
What do you think about the proposals? Would they raise standards, and help make pupils fit for the workplace, as the Welsh Conservatives have said? Or would they be divisive, and a backwards step, as critics have said?
The Welsh Government says it will "not be returning to divisive grammar schools".
It says education standards in Wales have not dropped since devolution - and it is focusing on breaking the link between poverty and low attainment.
Welsh Conservative leader Andrew RT Davies denies that dividing pupils into academic and vocational streams at the age of 14 would straitjacket students.
Welsh Welsh Conservative leader Andrew RT Davies explains to our Political Editor Adrian Masters what their new policy means.
He says the 11-plus is "divisive", and instead "14 is a far better time to make choices - and I use the word choices, rather than selection - so that people when they come out of school, have the qualifications that are fit for the 21st century."
The Welsh Conservatives have proposed a return to a grammar school-style system, where pupils are separated into two streams - academic and vocational - at the age of 14.
The Welsh Liberal Democrats say proposals, from the Welsh Conservatives, to reintroduce elements of the grammar school system here would just "see children cast aside when they're 14", rather than 11.
Aled Roberts says creating more grammar schools would "extend the attainment gap between pupils from affluent and less affluent backgrounds".
The Welsh Government Education Minister said "I thought someone was pulling my leg" in response to the Welsh Conservatives' call for a return to a grammar school system here.
Huw Lewis described the policy as "muddled" and "back to the future" on Twitter.