Remote Control Of A Linux Desktop?

Brian L. asks: "I am developing a product for Linux that is, in essence, a source code editor for a high school audience. Is there a way that the teacher could watch the screens of the students, and even interact with them (by stealing mouse and keyboard control to demonstrate a concept, for example) I've seen (shudder) iMacs do this quite nicely, but I have seen no such similar application for Linux. How could it be done?"