My brother's experiences reveal how overdue the advice is.
Last May, he was a relatively normal, moderately academic 13-year-old. Then at the recreation ground near our house, he was offered cannabis and agreed to buy some. This was the first time he'd had cannabis in his possession, though he later admitted trying a "puff" at a school party.
That evening he rang his girlfriend to tell her about it; she told another girl who gave him Pounds 10 to bring the cannabis into school.
Two days later he took it in and showed it to his classmates. But their reaction made him realise this was something more serious than swapping tapes or computer games, and he was beginning to change his mind about handing it over.
He didn't have the chance. A teacher discovered the cannabis on him. He quickly admitted it was for someone else, clearly thinking this would lessen the seriousness of his crime. Within half-an-hour he had been "indefinitely" suspended.
Next day it was announced in assembly that a pupil had been "excluded" from school and a letter was sent to all parents with the same message. At that time a formal inquiry had not taken place, and we believed the head was trying to pre-empt the result. In any event the inquiry backed her, and my brother was expelled eight days later.
The school was a Church of England comprehensive, converted from a grammar school. It's fair to say it was isolated from the drugs issue: in my time there, in the Eighties, I don't think the subject was ever raised beyond one vague letter and the odd general studies class. There was no clear policy and there appeared to be no need.
When my brother was caught, the headmistress was under pressure from staff and parents to maintain discipline. The realisation that cannabis had infiltrated the school must have come as a bombshell in this comfortable, middle-class corner of England. No mention was made of the two older girls who were involved - they were quietly let off with a three-day suspension. Later we learned that the mother of one was a senior teacher and the father of the other was a school governor.
As we are now aware, this kind of incident is not unusual in an age when opinions on soft drugs change by the year and research suggests one-quarter of pupils have experimented with cannabis by the age of 14. My brother was caught in the last few months before both schools and the Government came to a better understanding. Current advice says teachers should take prevailing opinion into account when dealing with such matters and that "rules must be reasonable in the light of contemporary standards".
It is not as if the seriousness of cannabis possession is self-evident. In an age when advertisers are still allowed to target smoking at young people (aided by Baroness Thatcher, no less), why should cannabis, arguably less dangerous, continue to be an illegal substance? The issue is so confused that even the police have mixed views, and tend to let off offenders with cautions.
Almost immediately after my brother's case, the school was forced to come to terms with realities which had changed even since I was a pupil. Many parents became aware their children had tried cannabis, some at school parties. It was painfully obvious that there were no rules in place, flaunting the 1986 Education Act which states that "the headteacher must make any behaviour policy generally known within the school".
In late November, my parents made these points to an exclusion appeal committee. We would have appealed earlier but the first inquiry had told us - falsely - that any further inquiry would not be binding. The appeal committee soon ruled that my brother's exclusion was precipitate and that he should be reinstated at the beginning of spring term.
By then, however, he had started at another school and we had no interest in sending him back to one which was still living in the past and which was so unconcerned about the welfare of a pupil in its care.