Teachers are pointing to a six point rise in the number of pupils attaining Level 4 or higher in their writing as evidence of the need to scrap SATs.
The publication of key stage 2 test results show that 81 per cent of children have achieved the benchmark in writing, compared to 75 per cent last year.
The figure is notable because there was no externally marked test this year for writing – the subject's score was based purely on teacher assessment.
The National Union of Teachers said the successful outcome showed that teacher assessment is a “robust" indicator of pupil achievement.
General secretary Christine Blower said: “The increased scores in writing, through the use of teacher assessment this year, have proven that it is a more accurate and fair way of assessing pupils' ability. We have long called for national curriculum tests at key stage 2 to be scrapped and replaced by teacher assessment which, when moderated well, is as robust an indicator of pupil achievement and progress as the current tests."
In total, 542,500 11-year-olds took SATs in May this year and other results showed a three per cent increase in pupils attaining Level 4 in reading – from 84 per cent in 2011 to 87 per cent this year. In maths, there was a four per cent increase on last year, with 84 per cent of pupils hitting Level 4 or higher.
Ms Blower continued: “The improvements in pupils reading and maths results are a credit to the hard work of teachers and pupils in year 6 and throughout the primary sector.
She warned, however, that the introduction of the year 1 phonic screening test could hit test scores in years to come.
She explained: “Pupils clearly have well-honed skills in reading for meaning and, let us hope, pleasure as well. Unfortunately, pupils lower down the primary system, being drilled for the year 1 phonics screening check, may be less proficient in these skills as they move through the school and the pressure to 'decode' text outweighs understanding."
Russell Hobby, general secretary of the National Association of Head Teachers, said it had been “another great year for learning in our primary schools".
He continued: " I hope our politicians will take the chance to praise the hard work of pupils and teachers rather than immediately turning their attention to trying to find the cloud around the silver lining."
Mr Hobby said the union continued to have questions about SATs and said that in light of the GCSE scandal the time had come to “look at the distortion endemic in assessment right across the board, from five to 18".
Elizabeth Truss, the newly appointed minister for education and childcare, said: “I congratulate pupils, teachers and families on their hard work and achievement. The government is committee to driving up standards by giving teachers more freedom, strengthening discipline and improving teacher quality."
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