Yet some five-year-olds now know more about drugs than their teachers, headteachers' leaders warned.
Judith Judd, Education Editor, examines the issues.
New advice from a headteachers' association warns schools that they should call in the police when they discover drug incidents but should not search or test pupils for drugs.
The guidelines on drugs, alcohol, tobacco and solvent abuse, the first to be issued by the National Association of Head Teachers for a decade, aim to promote a consistent approach to drug-taking.
Pressure to protect schools' reputation in a competitive market has made some heads reluctant to report drug incidents to the police.
Peter Walker, head of the Abbey School, in Faversham, Kent and a member of the Home Office drug education committee, said: "There are schools which wish to sweep the issue under the carpet but they are just keeping the lid on a problem that will explode."
David Hart, the association's general secretary, said: "No school in the country is a safe haven when it comes to dealing with drugs offences."
The background to the new guidelines, say the heads, are changes in society which mean that one child in two has experimented with drugs by the age of 15.
Liz Paver, the association's president and head of Intake Primary School, Doncaster, said: "Many children coming into schools are living in communities where drug abuse is rife. They come in educated about drugs beyond the education of their own teachers.
"Children who are involved in solvent abuse are getting younger and younger. Seven, eight and nine-year-olds in gangs are abusing solvents."
She quoted examples of a nursery school which had to sweep the playground every day for syringes and a school where a six-year-old told a teacher that she was sent to bed every night while her parents took heroin downstairs.
Mr Walker said that drug-taking started at a very early age. There were 12 solvents such as nail varnish and paint remover in most homes. Only about three or four per cent of drug-taking took place in schools.
The guidelines warn heads that they should not search children suspected of having drugs. Ms Paver said that searching children left teachers open to accusations of assault.
"We are in a position where parents can go to law and we have to be more careful than we used to be. Twenty years, ago I would always have cuddled a crying child. I wouldn't dream of doing it now."
If she suspected a child was concealing drugs, she would send for a responsible adult and ask them to do the searching.
The guidelines also advise against drug testing. Mr Walker said: "I would be worried about creating fear among youngsters, about the expense and about the possibility of encouraging youngsters to move on to harder drugs which were less easily detectable."
Heads should recognise that drug and alcohol abuse may be the sign of a child's problems and should not automatically exclude them, the guidelines say.Reuse content