A number of schools have been able to access their Sats results ahead of them being officially published because of a blunder on a government website.
The Department for Education confirmed that during testing of the Standards and Testing Agency’s system “a small number" school results from key stage 2 Sats were accessed.
The results were available on the NCA (National Curriculum Assessment) Tools site, which schools used to receive their results on Friday.
It is unclear for how long schools were able to access their results before the mistake was rectified.
The results are due to be published on the site on Tuesday 10 July at 7.30am.
A headteacher has criticised the mistake, which she said has given some schools an advantage.
Debbie Wylie, principal of Cramlington Village Primary, in Cramlington, near Newcastle, told Tes she was annoyed by the error that had given some schools more time to analyse their results ahead of the actual publication day.
Some schools 'get a head start'
“It gives some people a head start,” she said. “It just seems wrong when we have to follow so many procedures and rules to make sure everything is standardised.
“Then something happens in the administration and some people can get results early. If schools had done anything like this then our Sats results would be declared null and void. It just seems like double standards.”
A Department for Education spokesman said: "During testing of Standards and Testing Agency’s system, a small number of schools were able to access their KS2 test results in advance of the main release on 10 July at 7.30am.
“This was quickly rectified and affected schools have been advised to check the NCA Tools system on Tuesday 10 July to ensure they have final results.”
There have been issues in previous years with Sats papers being published ahead of the official tests taking place.
Controversy surrounded the tests two years ago when a key stage 1 spelling, punctuation and grammar test was published online in advance of most schools sitting it.