Avoiding a situtaiton such as presented in this case study should be the priority of all teachers, and since a classroom project such as a wiki would serve to provide numeous positive experiences, caution and planning need to at the forefront when exposuing our students to these tremendous learning opportunities. Thus, my earliest grade level recommendation for a wiki would be sixth grade because of the student's developing maturity and responsibility to take on such a task, as well as having a firm academic foundation to be successful.
Ensuring that all students are involved in the wriiting and editing process, as a proactive requirement, Miss Walker could have the group complete an outline of their project, indicating which student is responsible for what content. She can also monitor the wiki to see that each student has been contributing to it. Additionally, expectations of each team member need to be explicit, accompanied by full understanding on the part of the students, before embarking on this project.
Miss Walker's plan on teaching about plagiarism, while better late than never, should not be the only resolution taken. Prior to implementing Miss Walker's plan, I'd suggest she meet one-on-one with the students whom she knew plagiarized so they know that she is aware of and is watching plagiarism. While not being confrontational, she could allow each student an opportunity to explain, to discuss where their confusion occurred, and to briefly explain plagiarism as a precursor to her formualted plan. Additionally, as the adult and the teacher, Miss Walker needs to take the brunt of the responsiblity because of her failture to address plagiarism and her expectations prior to the assignment; thus, the students should be permitted to edit their work and learn from this experience. Making each of the students aware, through the one-to-one meetings mentioned previously, that they were 'caught' should have enough of a lasting impact upon them to prevent further plagiarizing. This experience should be a 'teaching moment' for both teacher and student. It would be good for he to admit to the class that she made a mistake; students need to see that teachers are also human.
Other concerns that I can envision with the use of wikis would include: a) the use of 'made up' material by the student rather than factual material because of the temptation to embellish since they will be considered 'published'; b) exercising control over the content of the material presented; and c) concerns regarding the wide spectrum of abilities (grammatical, etc.) of each student (i.e. a struggling writer may be negatively impacted emotionally or may expreience a tremendous amount of pressure to perform in such a 'public' environment).
As teachers, we need to remember that we can plan our best to avoid situations such as plagarism; yet, there will be times when the unanticipated will happen. Adapting to and learning from each of these experiences will further develop our confidence and professionalism which will allow us to become superb teachers.