Infant teachers lack the confidence to rely on their own judgement rather than national tests, Leeds university researchers say.
The researchers talked to 115 Year 2 teachers who were able to change this year's key stage 1 test timetable and base their final assessment of their seven-year-old pupils on their own judgement.
But most teachers involved in the pilot project did not take up the opportunity to test pupils at any time from January using last year's papers. Instead they chose to take this year's papers in May with the rest of the country.
Pupils would not have lost out from earlier tests because schools in the pilot reported only teacher assessments - made at the end of the year - rather than test results.
Professor Ted Wragg, emeritus professor of education at Exeter university, said: "People's confidence has been shot to pieces. This is what happens when you browbeat a profession for a long time.
"The high stakes of league tables and inspections have created a cowed profession when people for formal purposes follow everything to the letter, terrified of putting a foot wrong.
"It is like Brave New World where the people become defenders of the system that oppressed them. It is a 21st-century tragedy. The profession has to stand up and say to politicians to go and boil their collective heads."
Teresa Bain, senior inspector for primary assessment in Dorset, said: "Most of our schools did the 2004 tests. They wanted to have something to check with, given their added accountability. Primary teachers are devoted to doing their very best and getting it 150 per cent accurate."
The National Assessment Agency, which ran the pilot, said some teachers had created more work for themselves by providing more evidence to back up their assessments than was needed.
More than 4,800 schools in 34 local authorities took part in the pilot project.
Dr Matt Homer, of Leeds university, said: "The flexibility given to schools was not used as much as it might have been. Teachers' confidence in their ability to assess pupils is patchy.
"We spoke to some teachers at the beginning of the year and they were worried about it. In some places they relied very much on the tests."
Nigel Williams, principal officer at the assessment agency, told a conference in London: "The majority of tests were administered in May.
"Some schools were heavily reliant on the tasks and tests. Some teachers had provided a lot of evidence, we think too much. Local authorities need to make clear to schools what they need to see."
Ministers will decide in September whether all schools will now report teacher assessments for seven-year-olds, rather than the test results.
Wales has already scrapped the key stage 1 tests. Last week, the Welsh Assembly announced the key stage 2 tests will also be replaced with teacher assessments from next year.
Leader 14 Primary Forum 16