Secondary schools were this week given a one-year "breathing space" before the 14-19 learning pathways becomes a legal requirement.
But despite the delay being welcomed, there remain concerns the flagship initiative lacks investment.
Deputy education minister John Griffiths announced the pathways would not become statutory until September 2010 in the Senedd on Tuesday, admitting some schools would struggle to fulfil the requirements.
His step down on the progress of the learning and skills measure follows weeks of protests by heads, and two highly critical Assembly committee reports.
Last week, the Assembly's learning and enterprise committee reported it would be "unreasonable" to expect the new law to come into force next September. Earlier the finance committee attacked officials for failing to cost it.
But 2012 remains the final deadline when all schools will have to offer students at least 30 vocational and academic options.
Assembly members voted overwhelmingly in favour of the principles behind the pathways, intended to offer more choice to students and prevent teenagers dropping out of school.
But Gareth Jones, secretary of heads' union ASCL Cymru, renewed a call for a pilot scheme to assess the full cost of the initiative and its "real" impact on schools.
In the Senedd, Mr Griffiths also said teenage pupils may be given an explicit right to study in Welsh, admitting vocational courses were lagging behind in language provision.