More than a quarter of state school pupils in England are receiving private tuition lessons, say researchers.
Parents want children to have extra help in the hunt for school places
Parental worries about getting secondary school places is driving this growth in out-of-school lessons, says the report.
Research from London University's Institute of Education says parents are paying to give their children extra help with admission tests and exams.
Maths and English were the most common subjects for extra tuition.
The Institute of Education's report examined the extent of private tutoring in primary and secondary schools - and found that 27% of pupils were receiving extra lessons.
And your e-mail responses suggest that parents are paying about £15 to £25 for these extra lessons.
There were wide variations between different schools in the survey - with one secondary school reporting that 65% of of one year group were receiving private tuition - while a primary school had 59% of pupils receiving extra lessons.
27% of state pupils receive extra lessons
Parents worried about tests and school places
Up to 65% of one secondary school year group in survey receiving tuition
Only 9% of pupils have extra lessons for "additional learning needs"
Parents were most likely to pay for extra lessons when they were worried about competition for sought-after school places - in particular, it says that this happens in areas where secondary schools are of "uneven quality".
Among parents of secondary school pupils, extra tuition was focused on passing specific exams, such as maths GCSE, says the report, written by Judith Ireson and Katie Rushforth.
The survey also suggests that parents are choosing private tuition more out of anxiety than because their children have any specific weaknesses in lessons in school.
When parents of primary pupils were asked why they had paid for extra lessons - relatively few said that it was because their children needed to catch-up.
The most common reasons for private lessons was to give them an additional advantage in tests and secondary school entry exams - or else to help them to "learn subjects more quickly".
Cost not an issue
Much smaller numbers of parents used private tuition because their children were falling behind in school lessons.
And the widespread use of private tuition did not seem to be linked to any feeling that schools were not doing their job.
Fewer than one in five parents who paid for private tuition said that they were motivated by weaknesses with teaching in school.
An even smaller proportion - only about one in 10 - said that tuition was compensating for a lack of support from school.
The cost of tutoring did not seem to a big concern - either among those that paid for private lessons and those who did not.
Researchers had also asked parents their reasons for not using private tuition - and the most common reasons reflected a feeling that the school and family already provided enough support.
The cost of private lessons was not seen as a major deterrent by many parents.
The growth in private tuition has prompted debate about its fairness for those who do not receive extra lessons.
"For many families private tutoring is an affordable and flexible way to help their children, however this inevitably places others at a disadvantage in the education system," say researchers.
The report also points to earlier research suggesting that private tuition was a predominantly "middle-class activity" and that a typical user of tuition was an urban parent with a child in the final year of primary school.
A selection of your comments about private tuition.
I paid £20 a session for my daughter to have maths tuition before taking her GCSE. She had been predicted an E grade, but the extra tuition gave her confidence and self belief and she gained a grade C.
I am currently paying £10 per session for a little extra tuition for my year 6 son. He is due to sit the 11 plus in a few weeks time, and as the competition is so fierce, we believe that he needs all the advantages that we can give him.
Until there is something in between a very good grammar school and a very average secondary school, parents will continue to pay to help their children in every way that they can.
Anne Cuthbertson, Alcester, UK
I've not paid for extra tutoring, both my wife and I provide the required extra. I have also provided extra tuition for others. The report under-estimates the amount of extra tuition our children require.
Perhaps the government could pay teachers to stay on one evening a week to run extra lessons in deprived areas. It is likely that many would do this voluntarily anyway.
Julian Berks, Leeds, UK
I pay for my son to have a private lesson every week myself. While I admit that it's unfair on children whose parents can't afford it, I'm just doing what's best for my son. Surely that's just natural?
As a grammar school pupil myself, I know now that some were there simply because their parents could afford to train them up. Unfortunately, truly talented, bright children are denied this opportunity because of their parents' financial situation.
Simon Hardman, Edgware, Middlesex
We used private tuition to build our daughters' confidence in test taking. We felt that the school did not do enough to prepare them. The cost was £25 per lesson (half an hour) and really we couldn't afford it, but thought it important. Although I do feel that it does give a disadvantage to those unable to afford this.
Julia Chittell, London
If parents are paying for additional tuition should this also be something that university admissions tutors should take into account and make a higher offer to such applicants? A student at a poor school is bound to do above average if he or she also has the advantage of a private tutor.The higher mark has nothing to do with potential but simply good additional teaching.
Michael Trenerry, Truro, England
I paid for my son to have a tutor for the last year of primary school so that he would be able to cope better with his Key Stage 2 SATS. I contacted an agency and the lessons were £18 for one hour. Some children may not need additional tutoring but the secondary schools that I had in mind for my son required entrance exams and I do not think that my son would have passed them had we relied on just the teaching in school. It is all down to choice, you can either pay for a tutor or not.
Julie Taylor, London, England
I send my five-year-old son to private lessons once a week, my son is behind at school and the £20 a session price tag for helping him catch up seems reasonable. I do not think that "fairness" is really an issue - it is every parent's obligation to give their children every possible oppurtunity to succeed in their life ahead.
One of my sons has a private, half hour, lesson per week in maths. That short lesson has allowed him to move from stream three to the top stream in just a couple of months. What would be unfair would be for me to deny my son that opportunity all for the cost of a couple of pints of beer a week.
Chris MacDonald, Andover, Hants.
Being an accountant myself, I did spend on an average four to five hours per week for two months to help my son prepare for his GCSE maths which he took a year early. It was quite difficult juggling busy periods at work. It paid off as he got an A* ! Worth all the hard work. I did wonder as to the situation of other children who do not have parents who could help them.
Bala, London, UK
It's due to the fact I want my children to have the best, however sometimes it is difficult to pay for independent school, hence I try to cover the cost by giving one-to-one which costs me £30 per hour for the 11 plus. As a lot of state schools are not as good as grammar schools in my borough ... we try not to miss any chances.
Kay, Kenton, Middlesex
I arranged for my daughter to have a weekly tuition session in maths, just before she took her GCSEs. She was predicted a D and the tuition enabled her to achieve a C grade, and she went on to do A levels and is now at university. In return I taught her tutor's son English, so no money changed hands!
Angela, Ipswich, Suffolk