Headteachers say that "secret" guidance given to Sats markers should be made available to all schools.
The call comes after teachers took to Twitter to share their anger over numerous examples of answers in the spelling, grammar and punctuation (Spag) that they thought had been wrongly marked according to the official mark scheme.
But it emerged yesterday that markers had been given further marking guidance that was not available to schools – and that markers were told to get rid of after use.
Now Russell Hobby, general secretary of the NAHT heads' union, has called for all guidance to be published.
"All forms of marking guidance should be transparent and available to schools," he said. "You need to tell teachers this [the marking guidance] in advance, otherwise people feel the goalposts have shifted and what you are trying to do is catch children out rather than recording what has been taught."