I like Amy Guptill’s explanation of the “three story thesis” for concretizing the difference between a high-school level thesis and a college-level thesis. These slides review her examples and also break Ursula LeGuin’s “Carrier Bag Theory” thesis into three levels, since I introduced them to that around the same time.
Some students prefer to practice identifying three-story theses with artwork, which may have simpler messages. Kehinde Wiley works well for this. I write “Level 1” “Level 2” and “Level 3” on the board. Students summarize the message of each level on a Post-It and place it appropriately.