Julian, you have my sympathy. This is a really appalling thing to happen to your son. Drugs are not only happening at Whitgift but in every school, private or otherwise. It is no longer related to money as fixes are now very cheap for some drugs; and it is not a London phenomenon either, it is very much in the country too as kids have less to do.
Additionally, schools are increasingly controlling the actions of their pupils outside of schools and, as Julian points out, punishing when even the police would not have acted. My local policeman couldn't believe this had happened and felt it was ridiculous.
The way to tackle this would have been a significant suspension, followed by some pretty heavy duty drugs education, brutal if necessary. The whole cohort should have been involved in this. After THAT, it would be fair to issue a stern contract with students that if any such thing happens again within the time remaining at school, they will face expulsion.
Drug education is wholly insufficient. For this age group, it needs to be a little more graphic. But when I refer to age group, I realise that many parents need more education too. Many of the current parent generation indulged in some drug taking, often at college or university, and many still do. But drugs have moved on.
Part of the problem is that youngsters are finding it an easy way to earn money. With the advent of fees at universities, large numbers find this an easy way to help with loans (prostitution too is now not uncommon). So often, the children are offered drugs by their mates and this cascades down to schools too. It is easy for them to trust their friends as selling "good stuff". But of course, behind their friends, there is often an addict who is so desperate for a fix they will sell anything to support their addiction. The higher up the chain you go, the more people you find who have dragged little or weak youngsters into a drug habit and will keep them controlled through it or worse, violence or murder. Every buyer always thinks their source is safe and providing good stuff.
But we should also get this in perspective. In this country, the received wisdom is to teach our children to drink responsibly. It is not uncommon for parties from age of 16 to provide some amount of alcohol. But, if you read or listen to/read Aric Sigman who is an expert psychologist focussing on youth issues(lecturing to children and parents at many schools), he lists for us the ten most dangerous drugs. Alcohol sits firmly at the top. During his talk, he points out that in the UK we believe in teaching our kid to drink responsibly by introducing them to alcohol early.....and yet alcohol is responsible for more damage, accidents, fights and deaths amongst youth then any other drug. Further, he tells us that it causes damage to the developing brain up to the age of 24 and that the younger a child drinks alcohol, the more likely he is to develop of regular drinking habit through life. During his talks, he then points to the 6th most dangerous drug on his list which is cocaine. He then turns to the audience and asks parents when they will be teaching their children to sniff cocaine responsibly. The silence that descends on the audience is total.
In a nearby school, the very sensible head of many years (sadly recently retired and replaced by a man with little understanding or sensitivity) had a view he shared with new parents. He said that he knew the boys entering the school were bright because the entry tests were hard. But that between 10 and 18, many challenges could happen: illness, death, divorce, testosterone/teenage and, some may not turn out quite as academic as originally thought. Nonetheless, barring serious crime, the school committed to see them through to 18 and produce the very best individual version of themselves. He was wise to life and the things that happened in growing up.
He dwelt for a while on explaining that boys can do very stupid things in teenage and gave us an example of a top student with a good record of discipline who had been caught joyriding. This stunned both parents and school. He told us that boys took risks and thought they were indestructible. He didn't encourage it but was realistic enough to know it was common and should be handled as part of growing up. These are young people and, barring extremes, should have their misdemeanours handled firmly but with understanding.
Sadly, the change in the school has meant that more than four boys were asked not to return in 6th form as they had previously been suspended. This is expulsion in fact. Much like Julian's boy who had the chance to withdraw or be expelled...same difference...(and 9000 in IBM in the early 1990s offered "voluntary redundancy" or their life was made so hard they were sacked....)it all comes to the same thing, it's arm twisting and dereliction of handling the problem. In addition, one boy has been on a very strict behaviour bond for the whole of the sixth form under threat of expulsion as he had, (outside school and with an outside school friend) taken a short cut across a railway line (something often done by both adults and kids). Unfortunately, the friend tripped and was severely electrocuted; the boy had to deal with it, call out the emergency services and the whole experience was so traumatic (extensive surgery needed on his mate) that he is having to have therapy. But the school saw it as trespassing. Anyone with compassion and common sense would have thought the trauma of what happened was sufficient punishment (the police took no action). The boy had no discipline issues in school or history of bad behaviour. Another boy had suffered through a particularly extended and poisonous family breakup which caused him (as it often does) to fall behind. The boy had to have psychologist help and the Ed Psych reported the situation had been largely responsible for his academic issues. His GCSEs will be badly affected. Despite this, the school chose not to offer him a place in the 6th form, EVEN if he achieved the required grades; a request for a three year 6th form was also rejected. There were no discipline issues with this boy either.
It seems to me that these schools have lost sight of their role of educating and developing real young people, not only the highly intelligent and problem free. Anyone can do that. The skill is in handling teenage with all the warts and helping each young person make a success of it. It doesn't mean ignoring misdemeanours but it does mean handling them in a balanced and fair way.
What we have now are schools focussed only on image and results. It's easy to cast the first stone when your life has run without incident but that may be through luck rather than judgement.
Julian, you have all my sympathy as does your son. You have been moral and honest and a brilliant role model for him. You have shown courage in speaking out. As someone said earlier, I doubt very much it will harm his future. I wish you all the best.