Paddy Holmes, head of Ditchfield Park School, Petersfield, Hampshire, warned that young children were being treated "like young animals", as the census showed that two-year-olds are the fastest growing group in fee-paying schools.
Their numbers were up 27 per cent to 4,584. Proportions of three- and four-year-olds also increased sharply.
Mrs Holmes said: "We are really beginning as a nation to produce children treated in many ways more like young animals, staying with their mothers only as long as they are biologically dependent."
Some children were being sent to school in nappies because both parents worked or because their father or mother was a single parent and had to work.
Mrs Holmes, chairman of the Independent Schools Association Incorporated, argued that the number of fee-paying toddlers had increased because more mothers wanted to have children and a career. A private school (fees around pounds 600 a term for under-fives) might be the only alternative to a nanny.
"It works well socially and educationally. But we may well live to reap the dividends in emotional terms from children who are separated from their parents from 8am to 6pm from the age of two," she said.
Research over many years showed that the younger children were taken away from their mother or stand-in mother for many hours a day, the more likely they were to have problems later.
However, she argued that well-organised nursery education might be the best option if children had to be parted from their parents. Where such facilities were available, two- and three-year-olds were not given formal teaching but helped to socialise and play constructively.
Chris Evers, the head of Cheam Hawtreys School in Newbury, Berkshire, and chairman of the Incorporated Association of Preparatory Schools, said that parents were sending their children to school at two because they needed diversions for their energy which the average family could not provide.
Independent schools said yesterday that the feelgood factor had returned as numbers in fee-paying schools rose for the first time in five years. But the rise was only 0.6 per cent and the number of boarders continued to fall. The biggest increases were among the under-fives and pupils from abroad.
Fee-paying schools now account for about 7 per cent of the school population, about the same proportion as they did before the late Eighties boom. The number of secondary-school pupils, apart from sixth-formers, is still falling but prep school numbers are up. Last year, 15 new schools opened and only 8 closed. Spending on buildings, at pounds 551 per pupil, reached record levels.
The figures come from the Independent Schools Information Service's annual census and cover 464,990 pupils, 80 per cent of those in all private schools.
Boarding numbers were down by 3.5 per cent, the lowest fall since 1991, while day pupil numbers were up for the third successive year. The rise was 1.5 per cent, higher than in the previous three years.Reuse content