Leigh Johnson has a humorous post on what she can expect from students when teaching Plato's story of the Ring of Gyges. I teach the Ring of Gyges in both my Intro and my Ethics courses, in different ways; in my Ethics course, it is mixed in with a number of excerpts from the Republic at the beginning, to get students thinking about ethical matters at a more general level, and in my Intro course I bring it up in the context of looking at Plato's Gorgias. So, despite differences in the the context of teaching, I found much of what she said to be funy in a funny-because-very-true kind of way. I think I get a slightly greater variety of responses -- I always have at least one or two students who vehemently reject from the beginning the idea that Glaucon is right, for instance -- but pretty much everything she notes is something I've found in my own classes.
An interesting common pattern I've found is that students will often hold both that 'might makes right' is the way the world works -- they have difficulty quite expressing how -- but that this is not right; it's also common for students both to take the 'student relativist' path -- avoiding any discussion of truth as such, and holding that everybody's moral opinions are 'true for them' -- and yet still insist on a real direction of moral progress. (I suspect that this has something to do with the 'social construction' point noted in Johnson's post, but I hadn't thought of it in quite those terms before. It's certainly true that a number of my Ethics students later tend to like the Millian idea that morality is both made by us and yet also is governed by stable rational standards.)