Private tuition increases social inequalities, is of negligible quality and could have an adverse effect on the state school system, according to a leading academic.
Judith Ireson, professor of psychology in education at London University's Institute of Education, reviewed existing research (much of it her own) into the cost, effectiveness and uptake of private tuition in England.
Seventeen per cent of 15-year-olds in England receive one-to-one private tuition - just under the developed-world average. (In Tunisia, at the top of the private-tuition league table, more than 70 per cent of pupils receive extra lessons in maths.)
The main advantage of one-to-one tuition, Professor Ireson says, is that work can be tailored to pupils' needs. But, she adds: "To effectively tailor work to a student's needs calls for knowledge of the subject matter, a model of the student's current knowledge, and pedagogical knowledge."
Surveying 504 tuition agencies, she found that more than half employ tutors with no teaching qualification. More than three-quarters offer tutors who do not have a degree in the subject they are teaching.
"Parents told us that they found private tutors mainly through word-of-mouth recommendations, just as you might find a plumber or electrician," Professor Ireson says. "The onus is on the parent to check the tutor's background."
The average cost of private tuition is #163;24 per hour, rising slightly with key stage level. Tutoring often extends through two or more terms, so the cost per subject can rise to about #163;600 in total.
Unsurprisingly, the take-up of private tuition is linked to parental education and occupation. Parents in managerial and professional jobs, and those with degrees, are the most likely to employ private tutors for their children.
"A major concern ... is that it increases social and economic inequalities," says Professor Ireson. "Tutoring is very prevalent in areas where there is intense competition for places in popular schools, and parents who can afford tutors may be able to secure a competitive advantage for their children, thus closing down the options for students from less wealthy families."
The rationale for hiring a tutor is often confused. Most parents say they hire private tutors in order to ensure that their children perform well in tests and exams, as well as to improve their understanding and confidence in the relevant subject.
But a survey of 296 Year 11 pupils, controlled for family background, shows that tutoring in maths raises pupils' ultimate GCSE results by half a grade. By contrast, English tuition has a negligible impact on grades in that subject.
Meanwhile, many parents say that they are confident helping younger children with the primary school curriculum themselves. However, private tuition is as popular among the parents of Year 6 pupils as among those with GCSE-aged children.
Professor Ireson suggests that much of the Year 6 demand therefore comes from parents looking to prepare their children for the 11-plus test, common entrance exam or key stage 2 tests. "Many parents in England see it as part of their parental role to support their children's learning in school," she says. "Private tutoring may be a substitute, or extension, of that role."
But, she adds, there are potentially negative consequences not only for those children whose parents are unable to afford private tuition, but also for the schooling system as a whole.
"Teachers may put less effort into their classroom teaching when they realise that students will cover the work with their tutors," Professor Ireson says. "Students who cannot afford extra tuition miss out on this crucial preparation for the next phase of education."
One-to-one Tuition: an ideal context for learning? An inaugural professorial lecture by Judith Ireson, IOE Publications, #163;5
Judith Ireson: www.ioe.ac.ukstaffphdtffch_27.html
Tuition through the ages
Private tuition has existed almost as long as Western civilisation.
More than 2,000 years ago, before the first schools were established, Alexander the Great's father, Philip II of Macedon, hired Aristotle to tutor his son in science and medicine.
Initially, tutors were also charged with developing their pupils' minds and characters. They were therefore expected to be morally, as well as academically, upstanding.
Now that school-based education is almost universal in Britain, the role of the private tutor has become much more specialised: tutors are expected to supplement work covered in the classroom in one curriculum subject.
Though most is still conducted on a one-to-one basis, some tuition agencies run after-school classes. Tutoring is also offered over the phone and via the internet. In January this year, publishing company Pearson announced that it had bought a majority stake in TutorVista, an Indian online-tutoring company.
However, the majority of British tutees still receive coaching individually, and in person. As in ancient Greece, such tuition remains the preserve of the privileged.
England is one of several countries that now offers one-to-one tuition in school, as a supplement to classroom education.
The Making Good Progress scheme, launched in 2007, included one-to-one tuition in English and maths. Key stage 2 and 3 pupils who fell behind others in their class were offered 10 hours of one-to-one tuition.
Meanwhile, the Every Child a Reader and Every Child Counts schemes target low-achieving primary children for intensive one-to-one catch-up tuition.
Funding for the schemes is included in school budgets until summer 2014. However, the money is not ringfenced, so schools are not obliged to use it for this purpose.