Serious question: why is cheating unfair to the other students? Do you bell your grades? If a handful of students get 90 who should have got 70, will all the rest of the students see their marks drop 1 or 2% to compensate? If you don't officially bell, do you do so mentally (class average on that midterm was 82; I had better make the second one a little harder) ?
If not, then how is it unfair to the other students that some cheat? It is unfair to themselves since they will have the mark but not the knowledge to go with it. They will probably blow a job interview or two. They may struggle in next year's courses that assume they know this year's material. They are hurting themselves compared to genuinely learning the material. They cheat for one of two reasons:
- they don't care if they learn the material or not; it is of no value to them and they only want the mark
- they are unable to learn the material in the time they can allot to doing so
If you want to change their behaviour, you'll need to change one of these two things. Either show them how what they are learning will be of value to them, or find a way to help them learn it better.
Examples of the first:
- Today we will learn to normalize a database. This is a common technique when [whatever] and CSC 203, DSC 307 and most grad courses here all assume you're thoroughly capable at this technique
- The next few lectures cover this history and motivations of the X technique. I've heard that students who know this material well do very well in job interviews for Y positions, because the interviewers are always asking about this topic
- By the end of this term you will know how to ABC. This is the most common task assigned to new hires who've just graduated from our DEF program, which is why this course is required for all of you. While I hope you all get high marks in this course, what's really important is that you master the technique: there's about an 80% chance that you'll spend your first working year doing this, for an employer who won't help you if you find it difficult. The TAs and I are here to make sure you're comfortable with it by the time you leave us
Sure, this is work. As an adjunct myself, I don't always know what things I teach actually matter in what other courses the university offers - I don't have the curriculum memorized. I do have a little more insight into the job picture than some other profs. Still, you can figure this stuff out - ask the TA if you have one, for example.
Now the second part. Some cheaters are privileged self entitled brats who can't be bothered to put in the work. (My father taught someone who brought a servant to labs to do the actual physical work of the lab and couldn't understand why anyone would object.) Ignore them: whoever should have reached them at age 4 did not, and you probably won't now. But some are scared: if their average drops they'll lose their scholarship. They're finding it hard to keep up because they have a job as well as studying. Their parent or significant other is ill. They are hanging on to their position rather precariously and they do rash and wrong things because they think they have no choice. You can gain some insight into that mindset in another question: I was caught cheating on an exam, how can I minimize the damage? especially some of the earlier revisions where the OP explains why they decided to cheat.
So if you think someone has cheated and you don't want to use the official system, simply hand them a note that says "See Me" and a time and place such as "30 minutes before class, in our classroom" or "5pm today, in my office." When you have them alone say something like this:
I think you were really struggling in that exam. I have learned to spot facial expressions over the years and you did not have the material for this course cold, nowhere near. You may manage to pull off a decent mark, whether by guessing or some other approach, but I don't think you know everything you need to know. Don't think I'm calling you in to get you in trouble. I want to help you. What do you need to learn this material thoroughly? Would you like a one on one session to go over the test questions and be sure you understand how to solve them? I have some resources that provide the same material we cover in class but from a different perspective, would you like those? (Perhaps some prefer videos, some diagrams, some hands on practices etc.) Have you talked to the student resource centre about test anxiety, test taking techniques, studying techniques etc? Did you know that if you have demonstrable issues with, for example, multiple choice questions I can work with the student resource centre to construct an exam that's a more accurate measure of what you personally know?
The entitled ones probably won't even come to the meeting, but if they do, they will decline all your offers and get out of there as fast as they can. The desperate ones? You just might reach them.