New assessments for pupils as young as three have been criticised as too complicated after it emerged that teachers will be expected to monitor 114 kinds of behaviour.
Under the system being introduced in September children will be assessed within six weeks of starting the play-led foundation phase to provide a "snapshot" of their abilities.
But the guidance document lists 114 different types of behaviour appropriate for three to five-year-olds that teachers will be expected to look out for. Primary school heads and staff have said this is too complicated and have called for simplification.
Rebecca Williams, policy officer at Welsh-medium teaching union UCAC, said: "A baseline assessment is crucial. However, (this) is just not realistic or feasible - it is too much for teachers to monitor properly.
"The danger is if you are asking them to do such a complex and detailed assessment within the child's first six weeks their results aren't going to be thorough enough."
Anna Brychan, director of the National Association of Head Teachers Cymru, said her members were worried about the workload implications for foundation-phase staff.
"Though we strongly support an all-Wales baseline assessment scheme, we want to help to make sure it works well."
The assessment's six key areas include reading, writing, speaking and maths. But in addition, staff must identify whether children are able to put on a coat and if they can make intentional marks on surfaces - for example, by drawing in the snow with sticks.
The Cardiff Primary Headteachers' Conference has criticised the tests as "not fit for purpose" and its secretary Graham Renshaw, head of Pentyrch Primary, has twice written to education minister Leighton Andrews with its concerns.
Mr Renshaw said: "If teachers' time is being taken up going through a long checklist it is going to have a negative effect on their pupils' learning and well-being."
Although most pupils will enter the foundation phase at the age of three, some might not enter until they reach compulsory school age after their fifth birthday.
A Welsh Government spokesman said: "It is never our intention to over- burden our teachers with paperwork. The profile, which has been developed to support the assessments, 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."
Original headline: Teachers told to spot 114 types of behaviour in 3-to-5s