The author takes an academic (rather than hysterical) approach and acknowledges the ethical issues involved, but the seems to dodge them:
Drug testing, though, raises complex ethical issues. For example, whether young people can give their informed consent to be tested, whether testing impinges negatively on the teacher-pupil relationship and, perhaps most crucially, how you respond when a young person tests positive for illegal drugs. There are difficult questions to answer, but they are not so difficult as to rule out even trying to see if drug testing is an effective method of drug prevention. And if drug testing were effective would that mean we should mount a national scheme of regular testing? The answer to that question is no. What it would mean is that we could then begin a debate as to whether the ends justify the means, knowing that drug testing is at least one way of reducing teenage drug use.
I share his concern about heroin use among teens, particularly with the recent surge in fatal overdoses. However, I suspect that in most cases there are a lot of people maintaining an uncomfortable code of silence and others refusing to see something that frightens them. Part of the problem is that nobody knows what to do if they have a friend or loved on with a drug problem. Treatment has been decimated over the last decade or so. I can’t help but believe that teachers, parents, friends, etc. would be much more attentive and responsive if they knew that high quality help was easily available for anyone who needed it. It might make random testing of teens unnecessary.