Tom, you might want to use some of these discussion questions I found at http://www.cliffsnotes.com/WileyCDA/Lit ... um-43.html
I'm not sure if you are already covering all or some of these suggested discussion questions, but here they are for use as you please. I'd think any questions you decide to use would work well as it's one thread, but you handle it however you like.
ESSAY TOPICS AND REVIEW QUESTIONS
1. How is Walden an expression of the transcendentalist vision?
2. Is the claim that the narrator of Walden is an anti-social recluse a valid one?
3. Describe how the narrator's financial "economy" is expanded to a philosophy of life.
4. What makes Walden a unified work of art rather than a "collection of eighteen essays"?
5. Discuss the seasonal metaphor that thematically unifies Walden.
6. Consider the significance of Walden Pond as a symbol.
7. What is John Field's debilitating problem?
8. Discuss the narrator's attitude toward the state.
9. Describe the narrator's reaction to the railroad.
10. What is the significance of the spring thaw at the railroad cut?
11. As described in Walden, what is wrong with American culture?
12. Discuss the significance of the narrator's bean-field.
13. Discuss the significance of Thoreau's use of the "I" voice in Walden.