'Neurotic' parents have been warned they could drive their children to burn-out by sending them to private tutors.
Rather than helping them to higher levels of achievement, pupils risk being exhausted by work overload and therefore attaining less.
The warning has been made by a leading prep school teacher, Sebastian Hepher, head of Eaton Square School, central London.
He has taken the unusual step of writing to parents to warn of the dangers of academic coaching, saying it can cause widespread damage to pupils' education.
He claimed that rising numbers of 'neurotic' parents were enrolling their children in evening and weekend lessons to give them the edge over their peers in the race for places at top senior schools
In some cases, children as young as six are also given tutoring with a view to securing places at sought-after prep schools, he said.
But he warned that the process had a serious impact on children, leaving them overloaded with work, tired and confused, particularly when tasks contrast with those set by the school
In his letter, reported in the Telegraph, Mr Hepher said that tutoring for admissions tests often backfired as it gave children a temporary edge but left many struggling with the academic demands of school, having serious impact on later GCSE and A-level results.
"Children can be overloaded with work, parents can be misinformed of what a child needs in order to generate business," he said.
"Children can be taught methods and practices which are confusing to them as they may conflict with the systems employed at school, children who are tired at the end of the day are then further exhausted by the extra sessions, school work can be affected due to overload, homework can be affected due to lack of time, and so the list goes on."
He added: "In my opinion it also creates difficulties for the children later on in their educational careers.
"If a child is tutored extensively in the lead up to exams and pre-tests, genuine weaknesses they may have will have been masked."
He told parents that are considering using a tutor to contact the child's teacher to talk over the issue.
The private tutor should also liaise with teachers directly to make sure any work compliments tasks already being carried out in the school.
Parents were also told to ask themselves whether they believed the level of extra work could be maintained without overloading the child, adding: "If the answer to this is 'no', then perhaps look carefully at why the tutoring is needed."
However, Alexander Nikitich, founder of Carfax Private Tutors, said that 'responsible tutoring' could enrich pupils' education. He said criticism of tutoring was often 'groundless scaremongering, fuelled by paranoia'.
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