Primary teachers remain highly sceptical about tests for seven-year-olds, according to a new survey.
The survey by the Association of Teachers and Lecturers shows that three-quarters believe the assessments of key stage 1 children take too long and are not educationally worthwhile.
By contrast, most teachers of older children were happy with the extra work created by the tests and thought they were valuable.
The union says the testing workload must be monitored. It is urging the Government to consider adopting the Scottish approach which allows teachers to carry out KS1 assessments when they think appropriate instead of at a set time.
It says children should be assessed at the start of the key stages so that staff can use the results to improve curriculum planning.
The survey backs up research by the National Union of Teachers last year which found continuing worries over how much assessment disrupted classrooms. .
But the School Curriculum and Assessment Authority dismissed the ATL survey, saying that its sample of 185 teachers was unrepresentative. SCAA's own survey of 359 teachers last year, carried out by the National Foundation for Educational Research, found high levels of satisfaction with the tests.
The ATL found 62 per cent of KS1 teachers thought the extra workload created by the tests was unreasonable.
Peter Smith, the union's general secretary, said: "Teachers are doing their level best to deliver the national curriculum, but concerns about the tests raised by KS1 teachers in particular need to be addressed as a matter of urgency."
David Hawker, assistant chief executive of the SCAA, said: "There is growing confidence that the tests are settling down and becoming a valuable part of the information on pupils' achievements which we need to improve standards. "
The NFER survey found 95 per cent of its sample rated test manageability satisfactory or better, and similar numbers were happy with the quality and appropriateness of the assessment materials.
KS1 assessments involve written tests in arithmetic, writing and spelling in groups or classes which take about 90 minutes, plus an individual reading test estimated to take about 20 minutes.
The reading tests can be held any time from January to July, while the other parts of the assessment must be carried out in a set week in May.