Sarty has very specific scenes of becoming an adult and against the nature of his father that he could possibly become. The family had moved twelve times due to his father's proclivity to start fires and burn down barns ("twelve movings.") But the very last time that the father had asked Sarty to get a can of oil, in paragraph 89, Sarty had decided that enough was enough. He had thought o himself that he could "keep on" running from his father at the very last moment in which his father had asked his help in trying to burn down de Sapin's barn. He also thought to himself that "[he] could run on and on and never look back" and escape his evil father's ways and make a fresh start for himself.
Sarty also realizes in the end that after hearing a shot ring out, that perhaps his brother was shot but in crying out "Pap! Pap!" looking for his father, Sarty ends up tripping over his dead father's body in paragraph 108, and he immediately shouts out "Father! Father!" He moves from the boyish "pap" to the adult "father" and eulogizes him in such an altruistic way that Sarty has definitely matured throughout his ordeals with his father and his family.