Okay, so this one might only work on freshmen because they tend to be pretty gullible. Here's how it works.
I normally give notes over the persuasive appeals, Ethos (Ethical), Pathos (Emotional) and Logos (Logical). I know, I know. Notes. So boring! Like, OMG, when are we going to have some fun?! Unfortunately, notes (especially of the short, manageable variety) are still necessary for some students. The trick is to use the notes immediately to practice. And that's what we do next; we practice.
At the end of the notes, I put up a slide that says simply. "You have homework tonight. You need to use one of the three appeals from today's lesson to convince me that we should not have homework. You need to write at least a paragraph."
Now, I could have had them write a letter to a senator or the principal about some arbitrary rule they don't even care about. Homework? Homework they care about. A staggering amount of them wouldn't do the homework anyway, but it's the principal that they earned the right not to have to do it. Most of them write a full page working through their argument and asking their friends to read their essay to me explaining why they should not have homework. You can really see their wheels turning and watch as they sweat under the pressure.
Was I really going to give them homework? Eh, probably not. The point is that I never have to worry about making up some kind of homework for them to do. Inevitably, the class as a whole comes up with the best argument possible, using all three appeals.
Half of having students write, and write well, is to give them a purpose they care about. Writing to the principal about the dress code is pointless because they know their letter won't do anything. Half of them can't tell you who one of our senators are, let alone a law they are involved in changing. Homework? In my class. Oh, they care about that. And they know they can change my mind if they just try hard enough using these magical persuasive appeals I just taught them.