A quarter of parents are forced to raid their household budgets to pay for extra tuition in basic GCSE subjects, despite fees of up to £25 an hour.
Research from Mori, published today, shows that 24 per cent of pupils in England and Wales are taking after-school classes by the time they reach the age of 16, proof, according to critics, that the secondary school system is failing.
The figures do not even include piano lessons or other leisure activities. Instead, parents are paying out for help in the essentials: English, maths and science.
The research, covering more than 2,700 pupils, was sponsored by Sir Peter Lampl, the millionaire businessman and government adviser.
It concludes that families from minority ethnic groups are more likely to have paid for extra lessons than their white counterparts, and that the most popular subject is maths.
How much advantage is gained, however, is open to question. Boys seem to benefit the most, according to an earlier survey by London University's Institute of Education.
This showed that, on average, the grades of those boys receiving extra help went up by 0.4 per cent, enough to turn a GCSE D-grade into a C. But girls who had received out-of-school lessons showed little if any improvement.
The use of private tuition to bolster schooling has become a burgeoning industry. Famously, it was revealed nearly three years ago that Tony Blair and his wife Cherie had hired private tutors from the elite Westminster School to coach their two older sons, even though they attend the London Oratory School, a high-performing state school.
Sir Peter, chairman of the Sutton Trust educational charity, said: "The proportion of secondary school children receiving private tuition, particularly in their last year of compulsory schooling, is incredibly high. It shows that many parents who can't afford independent school fees are nevertheless prepared to pay something towards their children's education."
Sir Peter is pressing ministers to pay for bright children to attend private sector schools with strong academic traditions. His charity pays for an "Open Access" scheme at the private Belvedere Girls' School in Liverpool.
David Cameron, the Conservative education spokesman tipped by many as a contender to lead the party, said: "There's a lack of rigour in many parts of the education system and parents find themselves increasingly frustrated. These figures reflect that.
"Schools are not doing enough to stretch bright children or those in danger of falling behind."
A spokesman for the Department for Education and Skills said there is a new focus on providing lessons "tailored" to the needs of individual pupils.
"The Government has a clear commitment to stretching the most able and giving additional help to those at risk of falling behind," he said.Reuse content