This is an activity, guided with a PowerPoint presentation, that helps students understand what goes into an argument/persuasive essay. I've been using this activity with college freshmen, but I think it would work well for middle and high school, too.
All you need is enough bags of candy for each group. I usually divide the class of 20 students into two groups, but it could work with smaller groups as well.
My students LOVE this activity, and they get candy!