Test questions that appealed to boys are likely to result in a dramatic improvement in writing scores for 11-year-olds this year.
The TES contacted 70 schools and asked them to compare this year's key stage 2 results with last year's. The figures show that test scores are likely to rise in all subjects except maths.
Overall, the proportion of pupils attaining the expected level 4 or above has risen from 80 per cent last year to 83 per cent this year.
The proportion of pupils achieving level 4 or above in English rose from 81.5 to 83.9 per cent. Scores in writing improved dramatically. Almost 75 per cent of pupils achieved level 4 or above, compared with 65.6 per cent last year.
At Hazelhurst primary, in Bury, the proportion of pupils reaching this level in the writing test rose by 20 per cent this year.
Stuart Birtwell, head, said: "Writing was identified as a weak spot, and we concentrated on it. There's no magic formula, but in the past there were poor papers. This year, they asked questions children could get their teeth into."
Other heads agreed this year's writing tasks helped to boost grades. Pupils were asked to describe an imaginary lizard and write diary entries about a day trip.
At Anthony Curton primary, Norfolk, the proportion of pupils achieving level 4 or above rose from 32 per cent in 2005 to 72 per cent this year.
Sarah Durrant, acting head, said: "Boys tend not to do as well in story-writing. This year's non-fiction writing favours boys and children who struggle."
David Street, head of Carleton Rode primary, in Norfolk, agreed. All his pupils achieved level 4 or above in the writing papers.
"This year's test was more boy-friendly," he said. "Boys are more interested in factual stuff. We've also done a lot of targeted work, getting resources that appealed to boys' interests. Boys' writing has been an issue for a lot of schools."
In science, 90.7 per cent of pupils scored level 4 or above, compared with 89.2 per cent last year. Maths was the only subject in which results dropped slightly. In 2005, 79.8 per cent of schools surveyed achieved level 4 or above, compared with 79.2 per cent this year.
However, these scores suggest that the Government will still miss its targets for KS2. Ministers had set a target of 85 per cent of 11-year-olds achieving level 4 or above this year. Last year, 79 per cent achieved the level in English, and 75 per cent in maths.
By 2008, ministers would like to cut by 40 per cent the number of schools in which fewer than 65 per cent of pupils achieve level 4 or above. Chris Davis of the National Primary Headteachers' Association believes the fault lies with the targets rather than the schools.
"They were artificial targets in the first place," he said. "The Government may have to bite the bullet and accept that maybe we've reached a plateau.
"I don't think much store should be set on test scores. They're not that important. They're not GCSEs - they're no more than a snapshot."
Mick Brookes, general secretary of the National Association of Head Teachers, also questioned the usefulness of the tests.
"What does the level 4 gold standard mean?" he said. "If you're a few marks below, it doesn't mean that you can't read."
A spokeswoman for the National Assessment Agency said: "National curriculum tests go through a rigorous two-year development process to ensure they are clear, engaging, good-quality tests. We work hard to ensure the questions are at the right standard and that standards are maintained from year to year."