As someone intending to give his students a Wikipedia writing assignment in the spring, I would say that ease of grading is not really the most important point here.
It's certainly not the most important point. But it's a factor, and forcing yourself to wade through random edits all over Wikipedia seems like masochism to me.
My intended assignment is "Add 1000 words to Wikipedia."
Should be interesting. Do you think you could at least give us a heads up preferably with a list of usernames so we can keep an eye on things? Some might want you to actually walk the students through the Wikipedia policies, but depending on your goals this may be counterproductive.
Probably demanding that student work be released under the GFDL in general is not allowed. However, a single assignment to contribute to a specific project is very different. A lot of schools are big on having classes, particularly first year writing classes, apply the writing skills to a project other than a paper that will only ever be read by the professor. Wikipedia is a great choice for this.
I'm sure a school like Dartmouth has a rule about who owns the copyright of student created projects. Personally I don't feel it's right to force a student to release his work under a certain license, though. It seems too much like pushing an agenda. Maybe there won't be any objection, probably even as the GFDL is not very widely disliked. But the idea reminds me of those professors who force their students to run their papers through some plagiarism detection service, thereby licensing their works to the services.
Furthermore, it probably depends on the context. I'll be assigning the Wikipedia writing assignment in the course of a first year writing course focusing on intellectual property and copyleft. What was the Dartmouth professor assigning Wikipedia for?
COSC 4 - Concepts in Computing, a survey course for non-CS majors.
-Snowspinner
Anthony