The teacher for my C++ class in college was extremely lacking, and he would just copy/paste his tests from a multitude of textbooks and online resources (to the point that some questions were impossible to answer since he didn't include the image required for context). It wasn't uncommon for the class average for his weekly quizzes to be in the 'D' range.

Soon people started finding ways to cheat. At first we found he left the answer key for his web quizzes in the html source to be graded locally. Once he caught on that people were using it, he changed it to server side grading. We were able to extract that as well, but he never took any further precautions against it. To try and prevent him from catching on to the rampant cheating, we had an unwritten rule where you wouldn't get too good of a grade, usually B's or an occassional A-. He would single people out who got an unusually good grade, and that person would get glares from the rest of the class because we all knew they cheated and got greedy.

At the end of the semester for the final, me and my roommate had managed to become pretty competent in C++, but we knew his tests were a whole different beast. He provided a 500 question/answer study guide that would serve as the question bank of randomly selected problems for the final exam. We would be tested through a web form in a computer lab which wouldn't allow any other windows to be open, and he would be monitoring the class to make sure no cheating happens. Sounds like it would be hard to cheat, right? Our clever plan (which worked flawlessly) was to get into the lab early and copy the entire 500 question study guide with answers onto the clipboard. Once the test started we found one of the text fields on the exam, and pasted the clipboard into it. From there we could Ctrl+f search the study guide from within the testing window for any question we came across. Could have gotten a 100, settled for a 97.