Never grade based on what sticks
Wikipedia has fostered an open community where editors are encouraged to build on others' work. Student work may be revised or, in rare cases, removed entirely by other Wikipedians. Over the years, this has been the hardest part of the Wikipedia assignment for students and faculty to understand.
Instructors have found success by informing students early on and regularly that they're graded on the research process and quality of the work they add, not on "what sticks" in the article at the end of the term. This aspect of Wikipedia editing is simply out of the student's control, whereas they can control whether they complete each training module, research their topic, draft their work, participate in a peer review, and incorporate feedback into a final contribution. We encourage you to make these parameters clear to your students so they know that they will be graded based on their engagement with the processes of editing, not necessarily the “complete” product. After all, Wikipedia is a dynamic, continuously evolving resource.