More than a quarter of children aged between 10 and 12 cannot add two small sums of money without using a calculator, a survey has revealed.
Youngsters are leaving primary school unable to spell, add or do times tables and their parents do not have the time to help them, new research shows.
Around a third cannot do division or basic algebra while half do not know what a noun is or cannot identify an adverb. Almost a third cannot use apostrophes correctly.
Despite this, parents only manage to spend less than 10 minutes a day helping their children with their learning, according to online tuition service mytutor, which commissioned the survey.
More than a quarter (27%) of children surveyed could not add £2.36 and £1.49 to get £3.85; more than one in five (22%) could not use the correct version of "they're", "there" or "their" in a sentence; almost a third (31%) could not pick the correct use of an apostrophe from three simple sentences, and more than four in 10 (42%) couldn't spell the word "secretaries" correctly.
In addition, more than a third (36%) could not divide 415 by five and a quarter did not know the answer to seven multiplied by six.
Almost half of parents surveyed (48%) said they think their child is worse at maths than they were at the same age, and more than a third (36%) felt their child's English was worse than theirs was at the same age.
Almost four in 10 parents (39%) said they spend less time learning with their children than their parents did a generation ago - with only 30% spending more time than their parents did.
Nearly six out of 10 parents (59%) spend less than an hour a week learning with their children, breaking down to around eight-and-a-half minutes a day. One in five parents spend less than 30 minutes a week learning with their offspring.
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.
"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."
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 cannot spell simple plurals.
Mr Smith added: "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."
OnePoll surveyed 1,000 parents and 1,000 children on behalf of mytutor.co.uk in December 2011.
Shadow education secretary Stephen Twigg said: "Labour raised standards in Maths and English, with a focus on the 3Rs through initiatives such as the literacy and numeracy hours.
"In 1997, only six in 10 children reached the required standard Level 4 in English and Maths. By 2010, it had gone up to eight in 10.
"Clearly, as this reports demonstrates, there is still much to be done to ensure children leave primary school with a grip of the basics.
"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."