Teachers in England are stepping up the pressure on the government over national tests.
Teachers say their assessments should carry more weight
The biggest teaching union - the NUT - is balloting members on whether they should boycott the tests.
Now another group representing teachers is calling for an urgent meeting with the Education Secretary Charles Clarke to discuss their "deep concerns".
The Association of Teachers and Lecturers (ATL) says the tests can restrict children's learning.
And it is children who are already struggling in school who suffer the most, the organisation says.
Dr Mary Bousted, general secretary of the ATL, has written to Charles Clarke to set out the group's concerns and to ask for an urgent meeting.
"We believe the government is neglecting the professional expertise that teachers can offer throughout the assessment process," she said.
"Our members have deep concerns about many aspects of national curriculum assessment.
"There is an opportunity for the department to make real progress but only if it can engage the teaching profession in an open and constructive dialogue."
The letter comes as the NUT ballots its members on plans to boycott the tests, which are taken in May, by children of seven, 11 and 14.
The ATL says it is not opposed to assessment or tests but to the way they are being carried out.
It says not enough use is being made of teachers' own assessments of pupils and that the results do not give a full picture of a school's achievements.
Officials at the Department for Education and Skills say the letter will be given careful consideration.
A spokesman said, however: "We are not going back to the days when we had no regular information about how pupils were doing in school.
"Assessment is vital to ensure continued improvements in learning and teaching.
"It means that pupils' progress can be tracked enabling teachers to give pupils greater support and motivation."