Final answer:
Andy and David Wallace's son went on a trip with the nature program called Outward Bound, which emphasizes personal growth, leadership, and teamwork through outdoor expeditions.
Step-by-step explanation:
The nature program that Andy and David Wallace's son joined for a trip is named Outward Bound. Outward Bound is renowned for its outdoor education programs that focus on personal growth, leadership, and team-building skills through various challenging expeditions. These expeditions can include activities like backpacking, kayaking, rock climbing, and sailing. Outward Bound programs are designed to help participants learn more about themselves and to develop a deeper understanding of their capabilities.