by Eric Rauchway

academics should not beat up on Wikipedia quite so muchOpen U
... if you want to cite to Wikipedia nevertheless, it is wise to use the "cite this article" link on the left menu in "toolbox". It will provide you with the precise revision number of the article, so as to remove all doubt at what you were looking at when you decided to make reference to it. Today's featured article is "Triceratops"
http://en.wikipedia.org/wiki/Triceratops
However, if I were citing it, I would not trust that a version from some future date (the then most recent one) says what I think it should, so instead I would "cite this article" as:
http://en.wikipedia.org/w/index.php?title=Triceratops&oldid=116764152
using the revision id. The full citation page is at:
http://en.wikipedia.org/w/index.php?title=Special:Cite&page=Triceratops&id=116764152
To see how the article has changed, of course, you can view the history for the article and select different versions to compare the two side by side. See, for example,
http://en.wikipedia.org/w/index.php?title=Triceratops&diff=prev&oldid=104301989
and the introduction of a paragraph on phylogenetics, which is then edited to death. Just a simple example of how these articles really develop.
I hope you can share this technique with your students. It puts a lot of arguments about "junk" in Wikipedia to rest.