The key stage 1 grammar, punctuation and spelling test has been cancelled for this year following the accidental publication of the paper online.
The decision came after Russell Hobby, general secretary of the National Association of Head Teachers, called for the test to be scrapped this morning, saying the leak was a "serious error which undermines confidence in the administration of primary tests".
This evening schools minister Nick Gibb said: "On being informed of the breach yesterday, I ordered the Standards and Testing Agency to undertake an investigation into how this breach occurred. I have also commissioned a root and branch inquiry into the operations of the STA.
"In the meantime we have worked swiftly to find a solution to the administration of this year’s KS1 grammar, punctuation and spelling tests. To remove any uncertainty and clarify the situation for schools, I have decided that we will remove the requirement on them to administer the Key Stage 1 grammar, punctuation and spelling test for this year only.
"Schools will still need to submit a teacher assessment judgement based on pupils’ work in the classroom as has always been the case. However there will be no requirement this year for them to administer the KS1 grammar, punctuation and spelling test or use the result as part of that assessment. Our immediate inquiry has shown none of the other KS1 test papers have been affected by this error.
"This is a clearly regrettable incident and I am sorry for any concern it has caused teachers, parents or pupils.”
The news emerged this week that the sample guidance material published by the STA contained the words from the real spelling test, rather than sample test words.
Jennifer Coupland, chief executive of the Standards and Testing Agency, said: "We were made aware on 20 April that sample guidance material published by the STA, to be used with the modified version of the Key Stage 1 spelling test, contained the live test words rather than the sample test words. As soon as we were made aware, we removed the document from the website.
“We believe this issue has arisen as a result of human error by a member of staff within the Agency and a failure to follow appropriate clearance processes.
“An immediate review is underway to establish the precise facts and we would like to apologise to schools and parents for any distress caused.”
Russell Hobby, general secretary of school leaders' union NAHT said: “It emerged last night that the live test paper for the Key Stage One Grammar, Punctuation and Spelling (GPS) test has been available on the DfE website for several months and has been used by some schools as a practice paper. We have no way of knowing how extensively it has been used by schools and parents.
“We wrote to the Schools Minister Nick Gibb this morning, expressing our concerns and asking him to free schools from the obligation to use the test. In deciding to pull the tests for this year, the Minister has acted quickly and appropriately to address the issue. School leaders will welcome this approach.
'We reaffirm our offer to the government to work with them to develop a stable, coherent approach to assessment.”