Radical reforms of education for 14 to 19-year-olds in Wales must be better explained to pupils, parents, employers - and teachers.
Most people are in the dark about the implications of the Assembly government's learning pathways initiative, say the teaching unions.
There are also concerns over funding for the reforms and the feasibility of new learning coaches, intended to help teenagers stay on track with their studies.
Learning pathways envisages offering young people personalised study programmes built up from a wider choice of vocational and work-based courses. The idea is to keep more 16-year-olds in education or training.
An Assembly government action plan proposes a revised key stage 4 curriculum from September 2009, and for all young people to be offered a choice of work-related and general learning options by 2010.
A marketing strategy will be in place from October, but the Association of School and College Leaders (ASCL) believes this is too late, arguing that it will be difficult to convince parents and employers of the value of qualifications other than GCSE.
The ASCL's vice-president Brian Lightman, head at St Cyres school in Penarth, Vale of Glamorgan, said: "Work needs to start without delay. The Welsh baccalaureate has had a lot of publicity, but as for the rest of learning pathways, there are lots of people who know very little about it - both parents and teachers."
The National Association of Head Teachers Cymru has similar concerns.
Spokesman Chris Howard, head at Lewis Pengam secondary, Caerphilly, said public documents relating to the reforms have been too bureaucratic and "barely readable".
"There should be some high-profile launch initiatives to the wider public, not just to the education world," said Mr Howard.
"Parents and employers need to know what's going on, especially as this policy will have the effect of closing or amalgamating sixth forms. There needs to be a more cogent voice selling the vision to parents and employers."
Geraint Davies, secretary of teachers' union the NASUWT Cymru, added:
"These plans are so radical there's a need to re-educate a whole nation in terms of education post-14. It's important that is done before this plan is put into practice."
The Assembly government has set aside pound;41 million up to 2008 to support the introduction of learning pathways. The money is distributed via 22 networks serving each council area in Wales But ASCL, formerly the Secondary Heads Association, has also criticised the funding arrangements as a "major hindrance".
Mr Lightman added: "Virtually all the funding is awarded on a bidding basis. If you're trying to change the curriculum, it's no good bidding for something that will be a one-off payment, and that will not be there next year."
The ASCL is also critical of the proposal to train learning coaches, which it says is wasteful and ignores the existing skills of careers advisers and youth workers.
The first formal training of learning coaches started last month. The government aims to have 220 learning coaches trained by summer 2007, and says most are existing teachers, advisers and youth workers.
"We want to enhance the existing support for learners," said a spokesman.
He added there was a "preparatory" year to ensure parents understand the 14-19 changes before they roll out from 2007. Guidance is already available for practitioners, with a DVD and and leaflet for learners and parents due out soon. And funding will be pound;32.5m by 20078, and is expected to continue.