Private schools were accused today of offering state-educated youngsters little more than the "crumbs off their tables".
In a stinging attack, Ofsted chief inspector Sir Michael Wilshaw said that too many fee-paying schools do nothing more than offer the loan of a playing field, or some coaching for A-level students.
In what he called his "Lord Kitchener moment", Sir Michael called on private school heads to take the lead, support their local schools and dispel the perception that they "do not care about the educational world beyond their cloisters and quads".
In a speech to the Headmasters' and Headmistresses' Conference (HMC) annual meeting in London, Sir Michael said that state school teachers were doing their utmost to give their pupils the same opportunities as those who are educated privately.
And in what will be seen by some as a thinly-veiled attack, he said that inner city school leaders "haven't got the time to worry whether their children are climbing trees proficiently" because gaining qualifications is the one route out of poverty for their pupils.
"They would find it deeply concerning, almost insulting, to believe that some in this room felt that they don't worry sufficiently about a balanced education for their students," he said.
"They would feel particularly insulted if this criticism was coming from some educationalists who have the luxury of teaching children from aspirant and often well-heeled homes - homes that would make damn sure that their children passed their exams, even though the school afforded them the time to climb trees and gaze upon the beauties of life," Sir Michael said.
"Indeed, how many inner-city comprehensives have a tree?"
It is understood to be the first time that an Ofsted chief inspector has addressed the HMC.
Sir Michael told a defensive audience that too many state schools are still not good enough, with huge differences in the quality of education in various regions of the country and a "persistent blight of underachievement" afflicting many of the nation's poorest children.
Private schools have a major part to play in helping state schools overcome these problems, he insisted.
Sir Michael acknowledged that some independent schools are committed to doing so, but added "many more do very little".
He claimed that figures from the Independent Schools Council (ISC) show that 34 private schools - less than three per cent of members - sponsor an academy, and five per cent loan teachers to state schools.
"For the vast majority of independent schools, the commitment and resource is far less - a bit of coaching for A-level students, the occasional loan of a playing field," Sir Michael warned.
"I'm sorry to say, but the ISC's list of activities is hardly evidence of a comprehensive commitment to partnership with state schools. It's thin stuff. These are crumbs off your tables, leading more to famine than feast."
Sir Michael challenged private school heads to use their resources to help less advantaged state schools, and specifically called for them to sponsor academies, saying they have the knowledge and expertise to do so.
"Effectively, this is my Lord Kitchener moment - your country needs you, the state system needs you.
"There is a perception that the independent sector only does its duty when push comes to shove. That it doesn't really care about the educational world beyond its cloisters and quads and only reaches out when the Charity Commission, universities or government forces it to act.
"I think that's unfair. Some of you are doing excellent work. But I can understand why inaction in other cases can be misconstrued as indifference."
Martin Reader, headmaster of Wellington School, Somerset, told Sir Michael that he had been rejected by state schools when he approached them to offer support, saying some were "politically opposed" to private schools.
He called for the Ofsted chief inspector to write a letter to state schools setting out the reasons why they should form partnerships with the private sector.
Adam Pettitt, head of Highgate School in north London, accused Sir Michael of giving incorrect information.
Sir Michael had told the conference that Highgate formed partnerships with 21 local state schools, offering preparation for Oxford and Cambridge interviews and summer schools, but this stopped short of formal sponsorship.
Mr Pettitt said his school was sponsoring three academies, adding "I'm sick to death of the wrong facts."