Drug education classes are being offered to schoolchildren too late and are being taken by teachers who know less about illegal drugs than some of their pupils.
Many of the 2,049 11 to 16-year-olds who took part in a survey, conducted by the Trust for the Study of Adolescence, said that they had received their first lessons on the dangers of drugs after they had been offered or tried an illegal drug.
They did not feel that teachers should have to, or were qualified enough to, talk to them about drugs. They believed former drug users would be better-suited to the task.
The majority of the children had first heard of drugs at the age of seven or eight. The average age at which they had first been offered drugs was 13. By the age of 15 more than half had been offered drugs and more than a third had tried them.
Cannabis was the most commonly used drug. However, much of the advice and education pupils had received had focused on hard drugs or had taken a "just say no" approach to all drugs. A fairly typical comment from one 15-year-old girl was: "Yeah, it put me off the hard stuff . . . they're dangerous. But you know she (the teacher) couldn't really say anything about dope, about the risks. I felt OK about carrying on using it."
The Surrey-based study by Dr Debi Roker also found a strong association between drug use and the consumption of alcohol and tobacco. Much of the drug education had, however, dealt with illegal drugs in isolation.
Drug advice was also said to be infrequent, with the majority of pupils having had their last lesson more than a year previously.
Dr Roker, who presented her findings to the British Educational Research Association conference yesterday, said that despite such criticisms most children felt that drug education in school had been helpful.
"The credibility of those involved in drug education was, however, mentioned repeatedly." she said. "Of the seven schools in our study, only one included someone from outside the school in their programme."
Dr Roker said that many teenagers were worried that they would get into trouble if they talked about their own experience of drugs. "Many of them wanted an arena in which it was safe to talk about drug offers. They wanted more information and education and more talks and videos in schools and youth clubs. But they also wanted more private sources, such as leaflets and books in school libraries and in doctors' surgeries.
"One 14-year-old girl said, 'I certainly can't ask my parents, they'd just have a hairy . . . thinking I was addicted'."