A study by Roehampton Institute in London for the Association of Chief Police Officers found that while 96 per cent of forces in England and Wales were involved in drug education, practice was haphazard and very few had evaluated their schemes.
Some police officers were giving inexpert advice on issues such as the health effects of drugs. Some schemes depended on the enthusiasm of a few individual officers; in others, carefully developed by multi-agency groups, PCs tore up the script when they reached the classroom.
Some forces saw their drug education schemes as good public relations exercises without measuring their impact.
The report recommends that although it is important for the police and other agencies to be involved in drug education, schools should retain overall control.
Such schemes should be properly costed and evaluated - otherwise they could be dropped if they could not prove their worth.
"Drug education must be school-led and if the police keep stepping in and taking responsibility away, it's not going to be there in schools in the long term," researcher Louise O'Connor said.
Police involvement was most effective in the last years of primary school, before children started experimenting with drugs or forming mistrust of the force.
Drug Education in Schools: Identifying the added value of the police service within a model of best practice. Available from the Drugs Education and Prevention Research Unit, Froebel College, Roehampton Institute London SW15 5PJ, tel 0181 392 3065.