Asking the police to teach lessons on drugs was like inviting the vicar to teach youngsters about sex education, Richard Hammersley, director of the centre for behavioural aspects of health and disease at Glasgow Caledonian University, told The TESS.
"By linking drugs education to offending, the message is that drug use is uniformly bad and we abdicate any responsibility for getting them (young people) to make discriminating choices about drugs," he said. "But young people make these choices; they just do it without formal adult guidance."
Even teachers cannot be trusted to educate youngsters about drugs, Professor Hammersley said, in a keynote speech about adolescent substance use at the annual conference for educational psychologists in Edinburgh.
Those streetwise enough to know what they were talking about might not agree with what they were being asked to teach, while those who were drug- naive lacked credibility, he argued. "Cannabis is a drug that a large number of professionals of any kind have used or still use. But teachers would be foolish to mention this because they could be subject to disciplinary action.
"If it got back to parents, all hell would break loose and you could have the bizarre situation where an outraged parent comes in to complain that a teacher uses drugs when the parent uses them and the child does too. It's all about how you present yourself - it's not about reality."
Professor Hammersley also dismisses the use of ex-offenders to talk about their experiences because they fail to see that to teenagers regard them as "old gits" and not one of them.
Instead, he advocated peer education and a whole-school approach to substance misuse, akin to eco-schools - the approach taken to raising environmental awareness. "It's about being consistent."
But Professor Hammersley was accused of being out-of-date by Detective Superintendent William MacColl of the Scottish Crime and Drug Enforcement Agency, which runs an annual "Choices for Life" event for thousands of P7 pupils. The messages delivered about drug misuse in Scottish classroom are "far from just say no", he said.
"Quite a number of years ago, it was recognised that `just say no' won't work. Children and young people have to know the real risks attached to taking drugs. Cannabis is the most abused drug in our society. But it is not the cannabis that parents smoked when they were young. There is evidence to show it is getting stronger and consumption is linked to psychotic illness."
There are 15 reasons why people do not become dependent on drugs, Professor Hammersley believes, ranging from the substance being too expensive or hard to come by, to explicit moral beliefs which prohibit their use or having people important to them who are strongly opposed to them.
Schools could take these factors on board and use them to stop their pupils becoming chronic drug-users, he argued. Teachers, for instance, could become role models "strongly opposed" to substance misuse. The school could also adopt a strict - as opposed to a tokenistic - no smoking policy, thereby reducing the likelihood that substances would be available or that youngsters would have the opportunity to take them.
Exclusion, however, was not an effective means of dealing with substance misuse in school, Professor Hammersley felt, because it was highly unlikely that a young person would stop using drugs as a result of being excluded.