How did Holling use his family, the violent times, and his fears to change and grow as a person from the beginning of the story to the end?
The main character of The Wednesday Wars, by Gary Schmidt, is named Holling Hoodhood.
I don't think that Holling intentionally used his family, the Vietnam War, and his fears to change and grow. I think those things unintentionally caused Holling to change throughout the novel.
When the novel begins, Holling is a bit of an outcast. It's because he doesn't fit with either of the main religions of his school. He's not Jewish, and he's not Catholic. That theme of Holling being in the middle of things, but not a part of things, is seen throughout the novel. It's even present with his house.
". . . you'd come to my house. Which my father had figured out was right smack in the middle of town. Not on the north side. Not on the south side. Just somewhere in between. 'It's the perfect house,' he said."
Holling doesn't feel like he fits in at home either. Mom does whatever dad wants, and dad is so driven that he ignores paying attention to Holling. Holling's sister isn't much help either as she changes into the stereotypical "flower child."
Holling does not get first hand experience of the war, but he gets details about it from Mrs. Baker. Her husband is in Vietnam and becomes MIA (missing in action) at one point. It's Mrs. Baker's fears and worries about her husband that cause Holling to think differently about the war. If Holling didn't care for Mrs. Baker, then his thoughts on the war may not have changed.
It's Hollings relationship with Mrs. Baker that begins to change Holling the most. He goes from seeing her as an enemy to seeing her as a friend and, later, a confidant. He goes from hating Shakespeare to even acting in a play. He goes from not having many friends to having a girlfriend. He goes from not doing any sports to being a solid running athlete. Holling even becomes more of a provider and protector of his family than his father. That's evidenced by Holling making sure his sister is able to return home. Dad didn't even lift a finger.
I would say that Mrs. Baker and Holling's experiences at school (with his friends) were able to transform Holling from a student that didn't care about much, to a student who cares deeply for the people that are closest to him in life, which is different from "using" his family and such for his own growth.