Patrick Tobin, chairman of the Headmasters and Headmistresses Conference of 242 top public schools, also blamed trendy parents for failing to give their children moral leadership.
A survey from Exeter University commissioned by the conference and to be published later this year showed that heads put divorced single parents ahead of drugs and alcohol as the main source of serious pastoral and academic problems. For boarding schools, drugs pose a bigger threat than alcohol. For day schools, the reverse is the case.
Sex did not feature among the heads' worries.
At the start of the annual conference in Jersey, Mr Tobin, principal of Stewart's Melville and Mary Erskine in Edinburgh, questioned the government's claim that it was restoring family values. His comments came shortly after Tony Blair announced a Green Paper on the family.
Mr Tobin said: "I don't see the Government doing anything to affirm the family as they say they are. They are not giving tax advantages to marriage yet we have a greater degree of marital breakdown than other countries. There is no way schools can single-handedly tackle this problem. We have to look to government."
Most pupils from broken homes did not cause problems, he said, but almost every suspension or expulsion he had to handle was related to family background.
Generally, young people today were better behaved than they were 35 years ago. They related more easily to adults and were less rebellious than the long-haired generation of the Seventies who were now parents. "It is these parents who often generate problems because they don't know where they stand on too many issues."
Mr Tobin urged his fellow heads to pay particular attention to the needs of boys, struggling to keep up with a new generation of confident girls.
He also criticised the Government for narrowing primary education and warned of the dangers of a "Gradgrind" curriculum, full of facts and dates. "The Government's programme for primary schools has echoes of the Revised Code of 1862 which just got back to the basics.
"Already we sense a squeezing out of the inspiration which historically has distinguished seminal periods in education development," he said.Reuse content