It was just before 11am and my home was already as far from being an oasis of calm as I could wish for on a Sunday morning. With two minutes to go before the weekly visit of the tutor, it was a race against time to calm down my seven-year-old daughter. This was because Lily’s protests of "I hate her. I never want to see her again” were so loud, they would surely be heard by Caroline as she approached the front door below.

In between thinking of different tactics to coax Lily to be reasonable, the words "How has it come to this?” kept running through my mind.

After all, wasn’t I simply being the best parent by hiring a young, enthusiastic graduate with a first-class degree to give my child extra help in maths? There was also the fact that with the Seven Plus exams looming now Lily was nearing the end of her pre-prep, most of the other parents in the class had already hired a tutor. Wouldn’t my child be at a positive disadvantage without one?

In my heart of hearts, I knew where my child was coming from. Lily was already working hard enough in the classroom without having any more of her playtime interrupted with still more maths. Yet here I was, one of the growing number of parents helping to make tutoring one of the country’s fastest-growing industries.

A generation ago, private tuition in the UK was the domain of a small number of middle-class families helping their children struggle to keep up or pass key exams. In the intervening years, that little bit of extra help has become a must-have. Nowadays for many youngsters, the end-of-the-day school bell is only the start of the second shift.

A quarter of schoolchildren now get coaching – up from 18 per cent five years ago, according to research from education charity The Sutton Trust. From traditional one-on-one sessions to group classes and online courses, the market in this country is worth around £6 billion, with families spending an average of £2,758 a year.

But tutoring is far from the magic bullet so many parents assume it to be. When I started to investigate how the tutoring explosion was affecting our children for my book Taming the Tiger Parent, I discovered that, far from making our children perform better, it is all too often making them perform worse.

The principal reason is that tutors, who will happily charge anxious families £60 an hour or more, require no formal teaching qualifications of any kind.

These days, the most popular source of tutors is recent graduates from top universities. Put a low-performing pupil one-on-one with a tutor who does not know how to handle issues such as low academic self-esteem and a child’s confidence can slide even further.

Former head teacher and parent educator Noël Janis-Norton says that if a tutor is hired to work one-on-one with a child who is already doing well, there may be some improvement. But it can be a different story when it’s a child whose confidence has been knocked because they have been struggling with the subject.

Noël, author of the new book Calmer, Easier, Happier Boys, published by Hodder in February, says: "Tutors may be experts in their subjects and they were usually good students themselves. So they don’t understand why a child is getting stuck or how to simplify a topic – or how to give the child the skills they need to get unstuck. Instead tutors end up papering over the cracks to please the parents.”

Like teachers, tutors should be trained in child psychology. "If tutors don’t know how to deal with under-confident children they may resort to chivvying them along: ‘Come on… you know the answer…’ ” Noël says. "That will just encourage the voice in the child’s head which says: ‘I don’t know how to do this.’ ”

But schools are testing children sooner and more frequently, increasing parental paranoia. More than 10 children chase every place at the most sought-after grammar schools. To impress good universities, GSCE results must be sprinkled with A*s.

The race starts early. One nursery school head teacher told me in dismay of coaches being hired by parents to prepare their children for assessment tests for entry into selective private schools. The skills required included balancing, hopping and colouring-in.

For this, small children are being traumatised. "We’ve heard of young children locking themselves in the bathroom when they hear the tutor is coming, because from a ridiculously young age they associate tutoring with stress and misery,” according to Will Orr-Ewing, himself the head of Keystone Tutors, who recommends no child should be tutored before the age of seven.

Despite the early starts, the trauma and the vast sums being paid – not to mention the huge chunks of time tutoring takes out of our children’s childhoods – Barry Sindall, chief executive of the Grammar School Heads Association, says that in his 20 years as a head teacher, he has seen little evidence that students gain from tutoring.

"Usually, tutoring is used to repeat a process that the child has already got wrong,” Sindall says. "A great teacher will identify the barriers to a child understanding a concept. They won’t just repeat it over and over again, as happens with tutors, in the hope that the children will somehow ‘get it’.”

Sindall believes that 90 per cent of children who are tutored would have achieved that level of performance anyway. "Where is the empirical evidence that tutoring works, or that it has a positive effect on a child’s attitude to education?” he asks. "I can see very little of it.”

Judy Ireson, Professor of Psychology in Education at the University of London Institute of Education, led a study which looked at 3,515 children aged 11, 16 and 18. When results were averaged out, tutored pupils scored just less than half a grade higher in their maths GCSEs than pupils who had not been tutored. Enough maybe to lift a borderline candidate from a D grade to a C. But in subjects such as English, private tutoring was found to have a negligible effect on GCSE results for boys and girls.

As for my daughter Lily, she is now 12, and her maths is better than ever. Not because we have continued to throw money at tutoring but because we have finally found a school where the teaching is good, thoughtful and tailored to her skill level.

My own view is that the tutoring industry has whipped up anxiety even more than necessary and sold it straight back to parents for huge profits. But, as I discuss in my book, like many of the things that parents are doing to try and help kids stay ahead, tutoring is backfiring badly.

The time has come to stop viewing extra coaching as a necessary evil in our education system – and appreciate that stressed, unhappy children with no downtime don’t learn well.

Yet whenever I continue to ask parents why they have tutors for their children, they will continue to say: "We just want to do the best for them.” I’d argue that it’s time to question whether it’s having precisely the opposite effect.