The architect of Wales's assessment reforms, including the abolition of Sats, has warned they will fail unless policy-makers invest heavily in training for teachers.
Professor Richard Daugherty, who led the review group which recommended scrapping national tests for 11 and 14-year-olds, said teachers needed time and training to develop their assessment skills.
But a key challenge is whether Jane Davidson, the minister for education and lifelong learning, local education authorities and schools will give professional development the funding needed to embed the reforms, he said.
Speaking to delegates at a conference on assessment for learning, held this week at the University of Wales Institute Cardiff, he said: "Is the Assembly government going to resource the professional development associated with assessment for learning, and moderation?
"Unless it does, it is making a pretty good case for it not working, because the professional development element is essential for the system to work."
Assessment for learning, or formative assessment, occurs when teachers feed information back to pupils in ways that help them improve their learning or encourage self-evaluation. Summative assessment, such as Sats, gives a snapshot picture of pupil attainment at a particular time.
In her response to last year's Daugherty proposals, Ms Davidson said she wanted to introduce a system that put pupils at its heart, built on the professional judgements of teachers and focused on assessment for learning.
The abolition of Sats for 11-year-olds this summer, and for 14-year-olds next year, means pupil attainment at the end of key stages 2 and 3 will in future be measured by teacher assessment only.
Primary and secondary teachers will work together in school clusters to moderate KS2 assessments, while all secondary schools are expected to gain accreditation for moderating subject-based assessments at KS3.
Professor Daugherty said he hoped teachers would not talk just about curriculum levels, but about the "nature of the learning that goes into that level".
"I have been party to group moderation that has been highly centred on learning. But some moderation systems are terribly bureaucratic and functional."
But he acknowledged that implementing assessment for learning would, for some teachers, require a fundamental rethink of their practice.
In 2004, Sats cost Wales approximately pound;4 million. The Assembly government has allocated an in-service training day for the Daugherty reforms in both 2005-6 and 2006-7, and funding for teacher assessment training will also be available from school improvement grants in 2006-7.
The contract for ensuring assessment standards are maintained at KS3, worth pound;3-4 million over three years, was this week awarded to the Welsh Joint Education Committee. It involves moderating standards for all students at age 14 and verifying the school policies and practices.
Gareth Pierce, WJEC chief executive, said the contract included "an element" of professional training, and that there would be "feedback" conferences for teachers.