Children need to get out and play real games, the head says
Many children are living in a "prison-like environment" surrounded by technology, the chairman of the Independent Schools Association warns.
John Gibson says such experience does not prepare children for adult life and schools should challenge this.
Playing conkers and mending bikes helped children in later life, he told the ISA's annual conference.
Recent research suggests five to 16-year-olds are spending up to six hours a day online or watching television.
Mr Gibson, who is head of Stoke College in Suffolk, said "playing out" as a child and taking part in activities such as putting an oily chain back on a bike, or playing conkers, exposed children to emotions such as disappointment which would prepare them for adulthood.
In his speech to the conference, he said: "When your life is lived through images constructed by a technical genius from Silicon Valley played on a high definition screen I just feel it will be more difficult to experience those important rehearsals for adult life".
He went on: "When William Wordsworth wrote 150 years ago that 'shades of the prison-house begin to close upon the growing boy' I believed he was talking mainly about school.
"But today's prison-house is just as likely to be the home, a seductive, comfortable prison for boys and girls whose nimble fingers are adept at working their mobiles and computer games, but have never used them to play conkers."
He told ISA members - heads of independent schools in England and Wales - that they should offer children a diversity and excellence of experience to challenge the culture of technology in which they live outside school.
In doing so, they should always pay attention to assessing risk, while preparing children for the world they would grow up in, he added.
In a survey by Childwise research agency last autumn, 1,800 children were asked how much time they spent either watching television, on the internet or playing on games consoles.
The survey suggested the children were spending 2.7 hours a day on average watching television, 1.5 hours on the internet and 1.3 hours on games consoles.
A casualty of this amount of screen time had been reading, it suggested. The children questioned were spending just over half an hour a day reading.
In particular, older boys were resistant to reading, with 42% of 11 to 16-year-olds saying they never read books for pleasure.
However playing sport still appeared to be a major part of young people's lives, representing nearly five hours per week.