New assessments that will replace national tests for 11 and 14-year-olds in Wales have been criticised for being too vague.
Education minister Jane Davidson announced the abolition of Sats earlier this year and wants to replace them with teacher assessments and a "skills test" for 10-year-olds.
This week, the Assembly passed regulations that will remove the legal duty on schools to conduct key stage 2 tests. Similar moves to tackle KS3 tests are to follow.
But the National Association of Schoolmasters Union of Women Teachers Cymru said it could not agree to the plans as they lacked clarity. It wants the issue of tests and their replacements referred to the workload review panel, set up this summer, to assess the impact of government policies on red tape and teacher workload.
The General Teaching Council for Wales backed the proposed changes but said it was hard to comment because of the lack of detail in the new package.
The two bodies were among 414 individuals and organisations responding to the Assembly government's consultation document on its assessment changes.
Under the proposals, Sats will be phased out by 2008 with KS2 tests for 11-year-olds becoming voluntary next year. KS3 tests for 14-year-olds will be voluntary from summer 2006. Instead, teachers' judgements of how pupils are doing will be used to measure progress, as is the case now for seven-year-olds.
The assessments would be subject to moderation to make sure teachers agree with each other about standards.
Geraint Davies, secretary of NASUWT Cymru, admitted Sats were unpopular but said their abolition would leave teachers "faced with the unknown for a good few years".
"How can we agree the new skills test for Year 5 without knowing what it will entail?" he said.
Mr Davies said the moderation schemes lacked detail and suggested that teachers would be expected to justify their assessments to other staff in their own schools, within clusters of schools and to local education authorities.
The GTCW has similar concerns. It did not question the plans for moderation but said it was reluctant to comment "in the absence of details about the new arrangements".
John Valentine Williams, chief executive of ACCAC, the qualifications, curriculum and assessment authority for Wales, said: "We will be piloting any arrangements that we put in place. They will be built on best practice and will be subject to consultation."
Ms Davidson said the new system would be subject to further consultation.
She added: "Whatever system emerges will have due regard for teacher workloads, will put teachers and pupils at its heart, and will be fully checked and tested before being adopted."
Support for the abolition of Sats is widespread, but responses to the Assembly's consultation highlighted the scepticism about optional testing.
There was also concern over plans to require governors to put more details on teacher assessments in their reports to parents.
Ms Davidson's plans are based on the recommendations of the assessment review group headed by Professor Richard Daugherty.
It found the present system put teachers under pressure to teach to the test, narrowed the scope of the curriculum and adversely affected teaching and learning.
A full report on the Assembly government's consultation is now being prepared and is to be published on the internet.
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