Primary headteachers are warning of an unprecedented number of rejections in response to appeals over "unfair" key stage 2 test marks.
Schools across England have now received the results of marking reviews from the national qualification watchdog, with hundreds concerned at how few were regraded.
The marking of this year's national tests for 11-year-olds had appeared to go smoothly after last year's debacle, when results were delayed. But heads said they were unaware of any previous occasion when so many seemingly justified appeals had been rejected.
Headteachers can appeal to the Qualifications and Curriculum Development Agency (QCDA) against marking that they think is so poor that a child has been given the wrong level.
Most concerns this year related to the writing test, in which children had been asked to write a report about trainers. Provisional results show that English results dropped slightly this year, with 80 per cent of 11-year- olds getting the expected level 4.
Stuart Pywell, head of St Stephen's Junior in Canterbury, said his school had asked for 14 writing papers to be reviewed.
"The teacher who prepared the appeal was one of the markers for writing," he said. "But the writing marks remained unchanged except for one child, who had one mark changed.
"If they had all gone up a level, it wouldn't have made much difference to our overall English mark, but I wanted to appeal so I could address the issue of poor marking quality."
Huw Thomas, a headteacher in Sheffield, said that he sent 14 writing papers back but only two were put up a level. He added that his faith had been shaken when he realised that some children, who had spelt the word "enormous" correctly, had not been given a mark for it in the spelling test.
Adrian Hayes, head of Our Lady Immaculate RC Primary, Chelmsford, has called on the BBC Watchdog programme to investigate after his level 5 English scores dropped from over 50 per cent to 15 per cent this year.
When he complained, the result was widespread changes to the reading papers - which he had no issue with - but not one mark altered on writing.
He said: "The QCDA said it will not change the marks. You come up against this brick wall. This is an injustice that deeply affects parents, children and teachers."
Mick Brookes, general secretary of the National Association of Head Teachers, said the association had heard similar concerns from its members and wanted heads to contact them with their examples.
"There is a sense of injustice from our members," he said. "If I was the head of a school and received papers back that were badly marked and the poor marking was then confirmed, then I would ask an external consultant for their opinion.
"If QCDA is not able to reassure professionals in the system that there is fairness and accuracy in marking, then we will be forced to look at some independent system."
The NAHT is planning to take the evidence it collects to Ofqual, which acts as both the QCDA's sister agency and ombudsman.
Earlier this year it emerged internal checks had wrongly penalised good markers, causing delays. Following this, Edexcel, which ran the tests this year, decided to relax the rules on the margins of error.
The QCDA said that the review outcomes were final, although heads could appeal about the process.