Faisal Nasim's consultancy Exam Papers Plus, which provides resources to students, told CNBC that although he was aware of tutors being engaged for children as young as three, his consultancy provided services to students aged between 7 and 13.
"From the ages of seven onwards, it is rare for a child to be accepted into a top school without some form of preparation from either parents, pre-prep schools, tutors or a combination of these. The level required at the most academic schools is well above the national average and so there are often gaps to be filled," he told CNBC.
There was a "great deal of misinformation and ensuing hysteria surrounding the whole entry process," Nasim said and that problems can occur "when parents harbour unrealistic expectations and thus subject their child to undue pressure."
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The demand for his company's services was "overwhelming" as the competition for school places increased, Nasim added -- a factor that one schools admissions expert said was driving parents to "unnecessary and counter-productive" measures such as employing tutors for three year olds.
"I think there are some very exceptional cases where some preparation for a child as young as three can be useful – but I would see this kind of preparation as playing games and so forth," Susan Hamlyn, director of the "Good Schools Guide" advice service, told CNBC.
Hamyln said some tutoring services seemed to be exploiting parental anxiety over the competition for school places but that it was totally counter-productive for a child to be pressured to learn.
"The best thing for any parent to do a year before they are looking for their child to go to prep school is for the child to spend a good year happily socialising with other children and adults in a nursery where they'll learn to understand and collaborate," Hamyln added.
"What schools are looking for are children who are socialized," she said, "not ones that can do their ten times table."