A spelling test due to be taken by thousands of children in England has been accidentally published online months in advance, prompting a fierce backlash against assessment in primary schools.
The mistake was noticed on Wednesday by Charlotte Smiles, a teacher in south-east England, as her school conducted an official trial of the exam, when one pupil appeared familiar with the material.
It emerged the paper had been made available as a sample on the Department for Education (DfE) website on January 26, which a spokesman described as a "serious error" and "deeply regrettable".
The blunder has been labelled "farcical" by the Association of Teachers and Lecturers (ATL) while the National Union of Teachers (NUT) called for primary assessment to be cancelled for 2016.
Around half a million seven-year-olds will take the Key Stage 1 spelling and grammar tests in May when they are at the end of Year 2 and the results are used to measure the progress of pupils.
Ms Smiles' school was randomly selected to take the paper early to set a benchmark for national standards.
She said the error would give some students "an unfair advantage" and may "inflate" results at schools which had been encouraging parents to use the DfE website to prepare children for the exam.
Ms Smiles criticised the Department for Education for showing a "lack of management".
She said: "They are expecting us to hold very high standards in terms of administering and keeping these papers stored safely, locked away, so that it's supposed to give a true reflection of the child, which tests very rarely do anyway.
"And it makes a bit of a mockery of the whole system to have accidentally posted it online."
Shadow education secretary Lucy Powell described the mistake as "an insult" to students and teachers.
She said: "The incompetence of ministers at the Department for Education is breathtaking. They have created chaos in the assessment system, and to publish upcoming test papers online, before children have had a chance to sit them, renders the whole process null and void.
"It is an insult to the pupils and teachers who have been working hard to prepare for them."
Christine Blower, general secretary of the NUT, said primary assessment was "in a mess" and results "cannot be trusted to be a fair and accurate representation of children's learning".
"Ministers should look at the reality of the situation," she said.
"They should set aside their ideological preferences and acknowledge that the system isn't working. A decision to cancel the tests, and consult with teachers and researchers about a better curriculum, and a better assessment system for primary pupils, is an urgent necessity."
Dr Mary Bousted, general secretary of ATL, called for the DfE to "scrap these reforms" and "work with the profession" to design an assessment system.
She said: "The DfE's chaotic reform of assessment in primary schools has been plagued by an unacceptable string of errors, miscommunications and delays. Teachers have lost confidence in the department's ability to oversee and run these assessments to an acceptable standard."
She added: "How many more mistakes will the DfE make before they realise these assessments are not yet fit for purpose and their implementation is chaotic? Why should our children be put through these slapdash tests?"
A DfE spokesman said: "This is clearly a serious error and we have launched an immediate investigation to understand how it happened. The material has been removed from our website.
"Fortunately, this is a Key Stage 1 test which is provided to schools to support Teacher Assessment judgements. The data used to judge the performance of schools and the progress children are making at Key Stage 1 are teacher assessment judgements. The results of these tests are not collected.
"Nonetheless it is deeply regrettable that it has happened."
He added: "We ask that if anyone has seen the material, they do not share it further so that the test remains helpful for those teachers who have not yet used it with their pupils."