• Define explicitly what you consider cheating and what kinds of collaboration are acceptable. As the statistics in Reference 1 suggest, your students’ ideas about it are almost certain to be different from yours. If you don’t make your definitions clear, they will invariably default to theirs. In addition, consider giving the students a voice in formulating cheating policies. Students are more likely to follow rules they help establish than rules they have no say about.
• Follow your institution’s procedures for dealing with suspected cheating. When you yield to the strong temptation to handle it entirely by yourself, students you catch may not cheat again in your course, but since no one will be keeping track of their violations they will be almost certain to cheat in other courses. Plus, if there is an institutional honor code, support and enforce it. Strictly enforced honor codes reduce cheating.
• Be fair to your students and they will be more likely to be honest with you. When instructors give assignments and exams that are much too long or make any of the other “top four worst teaching mistakes,” students feel they are being cheated and many have no reservations about returning the favor.
In “How to stop cheating (or at least slow it down)”, Richard M. Felder