Janis Burdin, of Moss Side Primary School in Leyland, says the standard of marking is the "final nail in the coffin" for the controversial tests, which are being marked by Educational Testing Service Europe under a £156m five-year contract.

She is now demanding the papers be re-marked and claims to know of at least two other schools who are asking for the same thing.

She said: "From what I've heard the training of the markers has been unsatisfactory. "We got our papers back last week but we are not releasing the writing exam results – the children would be mortified if they saw what they got.

"The marking, especially for the writing exams, is absolutely off the radar, it is that bad. We've spent hours looking at this wondering what to do."

Child A wrote about Pip Davenport, a fairground inventor.

The paper said: "If he wasent doing enthing els heel help his uncle Henry at the funfair during the day. And had stoody at nigh on other thing he did was invent new rides.

"Becoues he invited a lot of new rides he won a prize."

Incredibly, this received one MORE mark than Child B's paper, which read: "Quickly, it became apparent that Pip was a fantastic rider: a complete natural.

"But it was his love of horses that led to a tragic accident. An accident that would change his life forever."

Both children were awarded five out of eight for sentence structure. But Child A was given eight out of 12 for composition and effect, while Child B received only seven marks.

It is the latest disaster to hit this year's SATs exams since American contractors ETS Europe took over, including crashes, helpline overloads and software problems,followed by delays and hundreds of papers being returned either unmarked or to the wrong addresses.

Ken Boston, chief executive of the Qualification and Curriculum Authority , said: "The papers have been marked largely by the same people who marked papers in previous years – teachers and other experienced local markers who know and understand curriculum, schools and standards."

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