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Half of children aged between 10 and 12 do not know what a noun is or cannot identify an adverb - while almost a third, 31 per cent, cannot use apostrophes correctly.
More than one in five - 22 per cent - could not use the correct version of 'they're', 'there' and 'their' in a sentence and more than four in 10 couldn't spell the word 'secretaries' correctly.
Maths didn't fare much better in the survey by online tutor, mytutor, with more than a quarter of children being unable to add two small sums of money without using a calculator as they can't do division and basic algebra.
Twenty-seven per cent of children surveyed could not add £2.36 and £1.49 to get £3.85. In addition, more than a third, 36 per cent, could not divide 415 by five and a quarter did not know the answer to seven multiplied by six.
Nick Smith, head of online tuition at mytutor, said: 'Maths and English are key skills for children as they enter secondary school, yet our study shows that many are already slipping behind their peers and could be lacking confidence.'
The survey of 1,000 children aged between 10 and 12 found that one in four did not know their times tables, a quarter could not use decimal points and two in five could not spell simple plurals.
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Almost half of parents surveyed, 48 per cent, said they thought their child was worse at maths than they were at the same age and more than a third, 36 per cent, felt their child's English was worse than theirs was at the same age.
Almost four in 10 parents - 39 per cent - said they spent less time learning with their children than their parents did with them a generation ago.
Only 30 per cent claimed to spend more time helping their child with their learning than their parents did.
And nearly six out of 10 parents - 59 per cent - spent less than an hour a week learning with their children - amounting to just eight-and-a-half minutes a day.
One in five parents spent less than 30 minutes a week learning with their offspring.
Mr Smith continued: 'Despite half of parents thinking their children aren't as good as they were at the same age, most parents only manage to spend fewer than 10 minutes a day reading with them, helping them with homework or doing educational activities at home.
'Addressing these shortcomings early can make an enormous difference to a child's school career, with tutored children generally making more than a year's worth of progress with just 20 hours of tuition.
'Hectic modern lifestyles are leaving parents with less and less time to spend learning with their children - whether that is helping with homework or other educational activities.
'Many think that their child's learning is suffering as a result, yet fewer than one in 10 of the parents we asked had used private tuition to give their children a boost to their learning - with many citing travelling time and a lack of suitable local tutors as reasons.'
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'But the Tory-led Government is ignoring the warning signals in this report.
'Instead of focusing on the 3Rs, they are cutting funding for programmes which provide one-to-one support for reading and writing. This means 9,000 more children will be at risk of falling behind this year alone.'
A Department for Education spokesman said: 'Getting the basics right at primary school is vital.
'That's why we are placing such emphasis on improving pupils' reading ability early on, using the proven method of synthetic phonics to teach children to read.
'We are committed to improving standards in maths - bringing more specialist maths teachers into the classroom and focusing on basic arithmetic.'
The survey results come as a government maths education advisor has urged that maths be compulsory for the majority of students, no matter what they are studying, up until the age of 18.
Government education adviser Professor Steve Sparks argues that all students who continue with further education after 16 should also take a new maths qualification alongside their other subjects.
He claims that teaching post-16 students basic maths and statistics is vital for them to be able to compete in the modern world.
Give them an abacus and teach them the Asian way to do basic maths... after a few years they can do away with the physical abacus and use a mental one. The end result will be crazy fast basic maths skills with little thought required.