The number of primary schools having their exam results scrapped because of maladministration has increased six fold in 12 months amid fears rules are being flouted to boost marks.
New figures reveal there has been a sharp rise in the number of exam results being quashed because of allegations staff or pupils have cheated, or not followed the proper rules.
Statistics from the Standards and Testing Agency (STA) show that 37 state primary schools had exam results for a whole year group binned last year, compared to just six the year before.
In total there were 511 cases of alleged maladministration in schools last year, compared to 370 cases in 2012 and 292 cases in 2011.
And the number of allegations of breaches relating to tests for six and seven-year-olds trebled from 25 in 2012 to 73 last year.
The Department of Education said it believed the rise was down to a toughening of rules imposed by the STA.
In the report, the STA says maladministration "refers to any act that could jeopardise the integrity, security or confidentiality of the national curriculum tests and the phonics screening check, and could lead to results that do not reflect the unaided abilities of children".
It said this includes test papers being incorrectly opened, children cheating, over-aiding of children by test administrators or changes being made to children's test scripts by someone other than the child.
A Department for Education spokesman said: "Ensuring pupils leave primary school having mastered the basics is a key part of our plan for education and parents must be confident their children's tests are being administered appropriately and fairly.
"Today's report shows allegations of cheating are dealt with seriously and strong action is taken where there is doubt over the validity of the tests.
"The figures show the vast majority of complaints about maladministration are found to be unfounded and this year's results were changed at only 85 schools, representing less than one per cent of the primary schools where pupils took tests."