More than half of teachers in an official poll said the writing test taken by 11-year-olds this year was too dull to inspire bright children.
The test, taken by 600,000 11-year-olds in May, asked children to base a story on four pictures of a boy queuing for a game.
More than half of 273 teachers polled by the Qualifications and Curriculum Authority felt the task was not suitable for Year 6 pupils.
The report by researchers at Manchester university concluded that some schools felt the task "was restrictive for the most able, dissuading them from any attempt at creativity".
Most concern was expressed about able children. Fifty-two per cent of those polled said that it was a fairly or very poor way of assessing whether children were working at the higher level 5.
Michael Morpurgo, the Children's Laureate, took the test for The TES and described it as "bland".
The English test also included a shorter task, to write a radio advertisement. Most teachers felt this was suitable for the age group. The test was changed this year and consisted of two compulsory tasks, rather than a choice of questions.
But 62 per cent of teachers questioned said the changes were not an improvement, and 60 per cent felt they did not have sufficient information and sample materials beforehand.
This year, 60 per cent of children reached the expected level 4 in writing, the same proportion as last year.