How+could+a+Professor+use+wikis+in+the+classroom?

How could Professors use wikis in the class room? Today wiki's are becoming more effective as a source of sharing information and have already been implemented into classrooms. Collaboration systems like this could allow a whole class to be interactive with each other outside of class and would also allow student to help students. No longer would the teacher have to be the primary educator as students could explain things to other students. Simple systems like this would allow teachers to post comments to students or ideas that were simply left out of class or need some further clarification. For example if one student left class a little confused on an assignment and didnt fully understand the concept of it. The student then could go to the class wiki and get a basic idea of what it is he is trying to understand.