If I were a teacher I would take the time to make school work not the same paper for everyone. In fact, I would probably have 4 or 5 versions for a class of 20 people, just to discourage copying. Instead, it would help enforce a better understanding of the topic. If they don't know what to do they can ask for help understanding why they can't get the right answer. Being a teacher is very important. You're passing on knowledge to students, and if you let them cheat, they are not benefiting and the education of the world goes down with each student that graduates.