Campaigners have claimed that the publication this week of teacher assessment results alongside the national test marks prove that national testing for 11-year-olds should be scrapped.
Heads' union the NAHT has pointed to the fact that the teacher assessment averages almost exactly match the result of the national tests as evidence that the key stage 2 Sats should be binned.
The average result from teacher assessments for England's Year 6 pupils found that 81 per cent of 11-year-olds reached the expected level 4, compared with 79 per cent last year. The test result was also 81 per cent, although last year's test result was 80 per cent.
In maths, 81 per cent of pupils were assessed by teachers as reaching level 4, compared with 80 per cent last year. The test result was slightly lower at 80 per cent this year and 79 per cent in 2009.
Teacher assessment results are based on individual teachers' judgements of what a child has achieved by the end of the year.
At key stage 1, the decision to downgrade testing came after a similar correlation was found.
Russell Hobby, NAHT general secretary, said that now the KS2 teacher assessment scores have been proven to be rigorous, tests should be used only to inform teacher assessment scores as they are in Year 2.
"The fact the teacher assessment results are so similar is a good sign that we don't have teachers making inflated judgments of progress. I think it justifies our stance and it is much cheaper than the system we have for Sats."
This year, one in four schools joined a boycott of the tests held by the NAHT and the NUT, which are opposed to the use of test results to compile league tables.
The Government has promised a review of the KS2 Sats, but has also announced they will go ahead as usual next year. Mr Hobby said that the terms of the review would be crucial in determining the union's next step.
He said: "The NAHT is not a militant organisation. We would much rather go into a review process than take industrial action."
Schools minister Nick Gibb congratulated pupils and teachers for achieving the highest scores ever - but he was still concerned that more than a third of children were not achieving level 4 in reading, writing and maths.
He said: "No one is saying that the tests are perfect. We want to discuss with the teaching profession and academics how we can iron out those flaws."
A Department for Education spokesman said it was important to have externally marked tests to give parents information about schools because there was divergence between teacher assessment and test results at authority and school level.
Divergent scores at local authority level were published this week - but the picture is clouded by the boycott. In Darlington, where tests were run in only 14 of the 28 schools, 81 per cent of boys tested reached level 4, but teacher assessment found only 73 per cent at this level. The NUT said the relationship between teacher assessments and test scores was not the issue.
NUT general secretary Christine Blower said: "If teacher assessment were to be routinely published it would run the same risk as the high-stakes tests, narrowing the curriculum as is evident from Sats results for English and maths."
- The KS3 teacher assessments show that 79 per cent of pupils achieved level 5 in English - up two percentage points on 2009. In maths, 80 per cent achieved the expected level, up one percentage point, and in science, 80 per cent reached level 5, up two percentage points.
81% - Proportion of pupils who reached level 4 in English.