Rather than discouraging your students from using Wikipedia entirely, ask your students to perform close reading analyses of Wikipedia articles, do their own original research (with guidance and institutional resources), and improve existing articles or create new ones. This exercise is scalable and can span an entire semester with scaffolded elements, or can be integrated into your course in more discrete and modular units. Students will learn to evaluate the fallibility of Wikipedia as a source, and improve it for public knowledge using their institutions databases and library collections.
How to use Wikipedia as a Teaching Tool (PDF)
With details about the 5 Pillars of Wikipedia, guidelines for designing your assignment, articulating learning objectives, and designing your syllabus.
Wiki Edu Resources for Educators
A ton of resources for instructors, including handouts, packets, subject guidelines, and contact information to WikiEdu staff.