Character Analysis
Victor has always been close to his father—or, closer than he is to his mother, at least. So when he learns that his father isn't his real biological dad, Victor is obviously disturbed. He doesn't know how this will change their relationship and isn't sure how much not being blood relations matters. Over time, however, Victor realizes that Mr. Vollmer is always there for him. He's a good dad—taking time off of work to go to the movies with Victor and playing ball with him even though he's not a great baseball player himself.
By the end, Victor decides that his father is the best dad that he could ask for and that being related by blood doesn't really matter:
My father on the birth certificate might have been Unknown but the tall man throwing ball with me in his white shirt with his necktie stuffed between the buttons was my father as far as I was concerned. He got his shiny dress shoes muddy when he stepped in the flower beds to get a ball. He always tried to do about everything in the world for me and he didn't even have to if you wanted to be official about it. (19.73)
It doesn't matter that Victor's dad's name isn't on his birth certificate as the father—Mr. Vollmer has more than proven himself as a good father. He's always there for his son, and that's what really counts. Just as Victor learns that his stutter doesn't define him, he also learns that biology doesn't define his relationship to his dad.