Holling's friends change him by offering him the unconditional love and support he needs to become a fully realized human being.
From reading The Tragedy of Hamlet, Prince of Denmark, Holling learns that instead of searching for one's self, one should instead be looking for a home. In other words, Holling understands that it is in allowing one's self to be loved by others, or finding a "home," that an individual finds his identity. Holling does not receive that kind of love in his disfunctional family, but fortunately is able to draw strength from caring people in his school community in order to reach his full potential.
Some of the friends who support Holling in his development are Meryl Lee Kowalski and her father, Danny Hupfer and his family, and Mrs. Baker. Once they get over the awkwardness of their attraction for each other, Meryl Lee and Holling become true friends, being comfortable partners in school projects and enjoying just hanging out together. Meryl Lee supports Holling by attending his performances and activities, and Mr. Kowalski gives Holling a ride so that he can pick up his sister at the train station after his own father callously refuses. Danny Hupfer shows his loyalty in a special way when he returns his autographed baseball to Mickey Mantle after the famous player treats Holling rudely, and Danny's family takes Holling home from the autograph event when Holling's own parents can't be bothered, commiserating in silence after Mickey Mantle rebuffs him. Mrs. Baker comes to Holling's aid time and time again, arranging a meeting for him and some friends with two members of the Yankees to make up for his disappointment at his treatment by Mickey Mantle, waiting with him at the hospital after he is hit by the schoolbus, and taking him to Opening Day at the Stadium after his father once again lets him down. Through the love and support Holling receives from his friends, he learns the value of caring from and for others, to the extent that he is able to provide for his sister what neither of them receive at home from their parents - someone to love them, and help them grow to become mature and productive individuals.