Dr Bob Acheson, chairman of the Incorporated Association of Preparatory Schools, told the association's annual conference in Harrogate this week that a "rampant cult of individualism" has corrupted views of family, religion and democracy.
"Our independence affords us the chance to lift the eyes of children from the gutter of the 20th century and to help them aspire to the stars," he told his fellow heads.
Attacking a general moral decline, Dr Acheson turned his fire on sex and violence in the media, the lack of respect for institutions such as Parliament and the Royal Family, and the prevalence of family break-up.
"How often does your blood boil when separating parents tell you in the cosy privacy of your study that they are about to to split up but that this won't, of course, affect the children?" he asked.
While adding that independent schools have no moral monopoly, he said that they should keep "the torch of moral firmness burning brightly as a new dark age threatens to engulf us".
Dr Acheson was cautious about the new Government. The association should take up Labour's offer of partnership in its crusade for higher national standards, he said. But the language needs watching: "The word 'crusade', for example, conjures up pictures of intolerance, of might being right, of myopic single-mindedness which runs the risk of becoming intellectual fascism, and this sits uncomfortably with a truly liberal democracy."
Overall, the conference found the prep school sector in a positive mood. John Morris, general secretary of the IAPS, said pupil numbers had increased for the third consecutive year by about 4,000 - a 3.4 per cent rise. The largest increase was among children aged between to and six.
While boarding numbers were down by 3.5 per cent, it was a smaller drop than in previous years. "Overall, the message seems to be clear. Parents in large numbers are still looking for a prep school education of high quality, based on recognised standards of teaching and discipline in small classes."
The association had won a small victory in extracting from ministers a promise that discretion would be exercised in maintaining assisted places through to 13 in those schools that made transfers at that age. "To date, contacts with the new Labour Government have been cordial and constructive, and it is to be hoped that promise of partnership between the two sectors will prove to be real and beneficial for children in the two-to-13 age range."
David Hanson, the association's education director, said he could see many areas where co-operation between the sectors would prove beneficial: the independent school staff could learn more about assessment, recording and reporting from their state-school colleagues, who could, in turn, be helped with specialist subject teaching and information technology.