This Boy's Life is the autobiographical story of Tobias Wolff's childhood and young manhood. Tobias, who changes his name to Jack to celebrate author Jack London, treks across America with his mother during the 1950s. Beset by hardships, Jack struggles with coming of age and with his mother's insecurities. He seeks futilely to reconnect with his distant and troubled father, then finally washes out of school and joins the army just in time to serve in Vietnam.
In 1955, Toby and his mother, Rosemary, are on their way to Utah to make their fortune by mining uranium. While in Utah, Toby changes his name to Jack in honor of the author Jack London and also to remove himself from his father, who abandoned Jack and his mother shortly after Jack was born. Jack's father is now living in Connecticut with Jack's brother, Geoffrey, a student at Princeton, and is married to a millionaire.
Jack shares an intimate closeness with his mother who, because of her own abusive childhood, habitually involves herself with violent and volatile men. First, there is Roy, Rosemary's second husband, who follows Rosemary and Jack from Florida to Utah. Rosemary moves with Jack to Seattle to get away from Roy, where she meets Dwight, who seems harmless until Jack moves to Concrete to live with him, where Dwight reveals himself to be cruel, self-centered and petty. Dwight criticizes and berates Jack for real and imagined flaws, and his rants are constantly at the forefront of Jack's mind. Dwight assigns Jack chores for no reason other than to exhibit his power and control over the household. Dwight also forces Jack to deliver newspapers and takes the money Jack earns for himself. The only time Dwight expresses a genuine interest in Jack is when he teaches Jack how to fight. Dwight is excited by Jack's display of aggression, especially because it will be directed against Arthur Gayle, a "sissy" who has a short-lived friendship with Jack.
Jack takes refuge in his unusually vivid imagination. Dwight's abuse and Jack's own general unhappiness in Concrete only fuel Jack's fantasies. Jack longs to escape from Concrete so that he can recreate himself, but he can only live the life he wants for himself in his own mind. Jack submits exaggerated applications to private schools, claiming that he is an A-student, star athlete, and good citizen. Jack is obsessed with the idea of himself as a virtuous and gifted young man, and is able to convince himself that his lies are the truth.
Jack has many dreams of running away, but he never succeeds in actualizing them. Jack's first real attempt at running away involves a plan to flee to Alaska with Arthur Gayle. Jack plans to make his getaway after a Boy Scout meeting in another town, but he ends up befriending a group of boys from another troop, distancing himself from Arthur, and being conned out of all of his money in a game of chance. Later, Jack tries to take refuge with his older brother, Geoffrey, at Princeton, but this plan is rejected as his brother is a graduating senior and Jack's biological father is out of the question.
Jack also writes to his uncle in Paris detailing the harsh life he endures with his stepfather asking to be taken in. When the issue eventually boils down to Jack having to be adopted, he refuses and stays in Washington with his mother.
Jack finally gets the opportunity to leave Concrete and start a new life when he is accepted to the prestigious Hill School. Mr. Howard, an alumnus of Hill, interviews Jack and serves as Jack's mentor. Later, when Mr. Howard and his wife have Jack fitted for a new wardrobe, Jack is warmed by their attention and affection, which he has experienced very little of at home.
Before Jack leaves home for Hill, he and Rosemary leave Dwight after Dwight shoves Jack in front of her. Rosemary arranges for Jack to live temporarily with his friend Chuck Bolger. Although Jack promises his mother that he will be on his best behavior while at the Bolgers', he breaks his promise and is caught stealing gasoline from the nearby Welch farm. Jack feels terrible about stealing from the Welches, but cannot bring himself to apologize, which infuriates Mr. Bolger. Mr. Bolger, arranges for Jack to work at the Welch farm, but the Welches refuse Jack's help.
Meanwhile, Chuck Bolger is about to be arrested for the statutory rape of a girl named Tina Flood, who is pregnant, presumably by him. The sheriff offers to excuse Chuck if he agrees to marry Tina, but Chuck refuses due to his dream of leading an "ideal" marriage and life. Chuck is on the verge of being sent to jail when he discovers that another of the defendants, Huff, has agreed to marry Tina in his place.
The summer before Jack is due to begin at Hill, he goes to stay with his father in California to spend some time with his father and his brother. Immediately after Jack arrives, however, his father leaves for Las Vegas with his girlfriend. When Jack's father returns, he is arrested and later committed to a sanitarium, where he remains for the rest of the summer. While staying with his mother for Christmas break, Dwight finds Rosemary at her new home in Washington, D.C. and tries to strangle her in the lobby of their apartment building. Rosemary knees Dwight in the groin, and he steals her purse and runs away. Immediately afterward, Dwight is arrested. It would be the last time Jack will ever see Dwight again. Not surprisingly, Jack cannot make the grades that Hill demands, and is expelled midway through his senior year. After he is expelled from school, Jack joins the army and serves in the Vietnam War.