that a couple of us have recently used with a local high school class.
There are no "right" answers to the CLDs that one produces for these, but students should be able to support what they include with evidence (verbal or written) from the article. They can also do research to find other links and loops not in the original story, or add links and loops from their own mental models of the situation.
I don't know, but maybe after doing a couple that you give them, you can challenge the students to go out and find "systems stories" on their own that they can use to create CLDs. You should look at the stories to be sure there is a "system" in them.