fears over increased workload have blighted consultation responses to widely welcomed moves that "put teachers back at the centre of assessment", it emerged this week.
Strike action has also been threatened by teachers' union the NASUWT Cymru if the burden of judging pupil performance becomes too much of a strain on members.
Consultation over proposed national assessment arrangements for key stages 2 and 3 in Wales closed last Friday. It marks another chapter in Wales's disengagement from a test-driven, external assessment system, starting with the abolition of Sats for 11 to 14-year-olds in 2004.
The new focus is on internal assessment, carried out by teachers and moderated by feeder schools at KS2. External accreditation will be used as moderation at KS3.
But concerns over workload and funding have so far put a dampener on the "commonsense" ideal of trusting teachers to assess their own pupils.
In the most damning consultation response, the NASUWT Cymru said: "The union has already received reports that the pilot schemes are imposing unacceptable burdens on teachers. This situation cannot be tolerated."
The Assembly government replied that workload and practical issues were at the forefront of its thinking, something the school work advisory panel would be looking at closely.
But Neil Foden, head of Ysgol Friars in Bangor, said teachers' planning, preparation and assessment time was in danger of being abused if more funding was not found to back up the new assessment regime.
Under the plans, teacher assessments will begin in springsummer 2008 - an extension of this year's original deadline.
Around 30 secondary schools are piloting the new arrangements, with reports of increased workload already taking their toll on tired teachers.
In response, the National Union of Teachers Cymru says it is pleased Wales is moving further away from a rigid regime of external national assessment.
However, it warns that the new arrangements will require more teacher time and funding.
So far, the Assembly government has provided just two additional Inset days in the 20078 school year to support teachers. It has also dropped proposals for new statutory skills tests for 10-year-olds, a key recommendation of the Daugherty assessment review.
However, it has delayed a decision on proposals for controversial Year 5 skills profiles on pupils to 200910. At the same time, pupil-level data from non-core subjects will be collected for the first time by the summer of 2010.
Anna Brychan, Welsh director of the National Association of Head Teachers, said: "The argument against Sats must not be undermined by a temptation to use skills test data in the same way."
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