Illegal substances are so prevalent that around one in 10 pupils in public schools has taken drugs recently, and under-age drinking is also widespread, with two in three boys and three in five girls using alcohol. The study of 2,400 pupils in 20 schools by the Headmasters' and Headmistresses' Conference comes as public school heads are expected to recommend that pupils should not be automatically expelled for drug use.
Research carried out with the help of the Schools Health Education Unit in Exeter found that the scale of drug-taking and drinking in public schools is about the same as that in state schools. But public school pupils are more likely to have been offered drugs.
Nationwide about one in three 14-year-olds and two in five 16-year-olds have tried drugs at least once.
However, public school heads underestimate the extent of both drug-taking and drinking among their pupils.
The report from a conference working party to be published this week says that boarding school heads worry more about drugs, and day school heads about alcohol, but both see parental divorce as the most serious threat to their pupils' well-being. Sex scarcely features as a concern.
Attitudes to drug-taking among public schools have been changing with some schools putting more emphasis on education and less on expulsion.
Vivian Anthony, the conference's secretary, would not disclose any details of the report but said: "We have been trying to move people away from thinking that the only reaction to any involvement in drugs is automatic expulsion. It may sometimes be appropriate. There may well be circumstances in which that policy should be adopted with a good deal of care."
At present about 100 public schools carry out tests on pupils suspected of drug-taking. The working party wants heads to be flexible. Its view that any pupil involved in drugs should lose the right to be a member of the school community but may remain, subject to random tests, is expected to be reflected in this week's report.
However, a number of heads are expected to stick to their hard line of expulsion for anyone found with any illegal drug.