Primary school heads have criticised new assessments of Wales' youngest pupils as "not fit for purpose".
The tests will measure children's ability when they start in primaries in September, and what they will need to learn over the next four years.
In a letter to Education Minister Leighton Andrews, the Cardiff Primary Head Teachers Conference said the tests offered "no consistency".
The Welsh Government said they provided a "valuable snapshot" of ability.
The baseline assements are designed to measure what children have learnt after four years of the foundation phase, the learning-through-play initiative used in primary schools in Wales.
In October 2010 the Cardiff Foundation Phase Headteachers Task Group wrote to Mr Andrews, outlining concerns about the "lack of clarity and transparency" in the process of developing the Foundation Phase Assessment Profile.
But, after receiving the assessment documents two weeks ago, it saw that its suggestions had not been taken on board.
In another letter to Mr Andrews, the CPHC said it had "serious concerns" about the tests, which would have "a negative effect on children's learning and well-being".
It claims that "there is no consistency across the foundation phase" and that the links to outcomes are "either inaccurate or tenuous and do not support the standards agenda".
The group says that teachers are also concerned about the additional workload involved, as the assessment arrangements have not been piloted, and it is now calling for an urgent review of the procedures.
Graham Renshaw, head teacher of Pentyrch Primary School, called the tests "very bureaucratic".
"It's taking the teachers away from supporting the children in those crucial early days in school, when they need emotional support as they settle into full-time education," he said.
"The plans for the assessments were only announced about two weeks ago and they start this September so there is not much time."
A Welsh Government spokesperson said it was not the intention to "overburden our teachers with paperwork".
But she added the baseline assessments are "wholly necessary as they provide a valuable snapshot of a child's ability when entering the Foundation Phase".
"This allows practitioners to better plan for the individual needs of children and assists in the early identification of children who may need additional learning support."