I would strongly suggest that the TA require the students to fold their answer sheet in half, and keep it CLOSED. They should ONLY open the answer sheet when their pen or pencil is connected to the paper, and when they've answered it, close the paper immediately. While very few students actually cheat, sometimes, well, someone will accidently flash you an answer. As a TA, if I see a student with a paper open, I make a general class announcement to remind them to keep papers closed. If there are less than ten students, I don't require them to 'rotate' from station to station. I do ask them to be polite, and not hog a station if they don't know the answer. I also ask that they not crowd up behind someone working on a problem because they might see the answers. Generally, I find the Aggie students (compared to my undergrad!) to be more considerate and understanding of this. For questions that take longer to answer, I make two or more copies of the question to be set out during the exam. When I am no longer a TA for the course, the new TA may email me to ask me for help with the exam, and I'll tell them what's what to set up the answer key...there may be one in the test if I can find it. ;o)