Around 200,000 11-year olds will be starting secondary school next month without having reached the expected standard in reading, writing and maths.
This figure, taken from results of national SATS tests earlier this year, means that more than one third of children are not meeting the targets set by the Department of Education.
Just 65 per cent of 11-year-olds reached Level 4 (the expected standard for their age), according to the results.
Boys fell further behind than girls, raising fears that many will fail to cope at secondary school.
The government has pledged a return to traditional lessons in English and maths, including a fresh focus on the 'synthetic phonics' reading scheme and arithmetic.
Yesterday's results came amid controversy that more than a quarter of primary schools in the UK refused to carry out SATS tests this spring as part of a campaign to scrap them.The Government was unable to publish authority-wide results for 20 local authorities.