A revised timetable for the roll-out of Wales's new play-based foundation phase confirms it will not be fully in place until 2010.
Jane Davidson, education and lifelong learning minister, explained why she had been forced to postpone the pioneering initiative at the sixth annual congress of the National Primary Centre Cymru (NPCC).
She told delegates at the Listening to Learners congress, held at the Education and School Improvement Service centre in Toy Dysgu, Treforest, that more extensive piloting, a recommendation of the School Workload Advisory Panel, was crucial to its success.
Ms Davidson also said the extra time would ensure teachers were fully trained, as well as making sure there were enough staff. According to the new timetable, the foundation phase will become compulsory for three to five-year-olds by September 2008.
By the end of September 2009 it will be extended to all five and six- year-olds. However, it will not become mandatory for all age groups until the following year.
Ms Davidson said: "The timetable was very ambitious and proposed a rate of change to the curriculum and its mode of delivery and management.
"By starting with a pilot phase we have afforded ourselves the opportunity to adjust the period, scope and the roll-out."
The National Union of Teachers Cymru welcomed the delay, saying that it is essential to get it right.
Dr Heledd Hayes, education officer for NUT Cymru, said: "The original timetable was a little over-optimistic. Such a skilled initiative needs properly-trained teachers and staff."
But Geraint Davies, Welsh secretary of rival teachers' union NASUWT Cymru, said schools that had planned to be in the pilot programme next year should be supported.
He said: "Many schools had budgeted and planned for starting their pilot scheme at the end of 2006. I hope they will now be supported and not left high and dry."
Some of the other reasons put forward by Ms Davidson for postponing the initiative were:
* to ensure guidance material was fit for purpose;
* to take on board recommendations from the second year of monitoring and evaluation;
* to provide time for the consultation and legislative procedures;
* to ensure it fitted better with ACCAC, the Welsh qualifications, assessment and curriculum authority's national curriculum review timetable.
The Welsh Assembly has promised an extra pound;2.5 million in 20067 for the initiative, further topped up in 20078 with another pound;7.5m.
Pilots were set up in 41 schools in 2004, and an interim report by academics shows overwhelming support. Delegates at the NPCC congress were praised for raising standards in primary education.
However, Ms Davidson said a repeat performance was needed at key stage 3 to have "across-the-piste" good results.
The NPCC, a national charity, was set up to create a bilingual, collaborative organisation for Welsh teachers in line with a UK aim of developing good practice in primary education.