Like the web in the early days?Not quite ... I guess it's still possible to "wander off" on the web now!
This where design comes in...?
I wonder if we're talking at cross purposes ... I was thinking that it's very easy in SL to enter a search term, to teleport off there, and not really know where you are, but to gain experience of the range of users, of the different types of environment etc. When it comes to designing your own area, clearly you can make your island really innovative, so that students don't want to go exploring, but we can't (and I don't think any one would want to!) stop them going off.
(Of course, you then may have to spend some time getting all the students back to "home" if they've not figured out the landmarking system!)