This book is about a kid named Donald Zinkoff who is different from the other boys and girls. After years of being called loser, he finally gets accepted for who he really is.
The book begins with a young boy, who is soon revealed to be Zinkoff, leaving his house for the first time. He gets his first taste of freedom, and celebrates by running around and racing other kids. Even though he always loses those races, he is too enthusiastic and oblivious to notice.
The majority of the novel follows Zinkoff going through elementary school. When Zinkoff enters the first grade, he instantly does not fit in. His sloppiness and overall surplus of excitement is noted by his teacher, Miss Meeks. Despite Zinkoff's quirks, Miss Meeks instills confidence in him as well as shows him the wonders of the "Bright Wide World" at his age. She looks past all of Zinkoff's oddities like his giraffe hat and his chronic laughter and sees him as the fun-loving child he is. Zinkoff's second grade teacher, Mrs. Biswell, is the opposite. She scolds sloppiness and lack of discipline, so, unsurprisingly, she grows a deep hatred of Zinkoff. However, despite Mrs. Biswell's attempts to reduce Zinkoff's spirits, Zinkoff remains as light-hearted as ever. He also takes up soccer, and even though he lacks any skill, he still enjoys the game more than the others, who only care about winning. While in the second grade, Zinkoff bonds with his loving father by following him on his mail route. Zinkoff has to stay home for the first few weeks of the third grade due to recovery from surgery. Overcome with boredom, he tests his courage by trying to walk downstairs to the cellar with the knowledge that the Furnace Monster dwells at the bottom.
Zinkoff's life begins to take shape once he enters the fourth grade. In the fourth grade, Zinkoff gains a positive reputation for the first time in his life. Mr. Yalowitz, his fourth grade teacher, is the first of his teachers to truly understand Zinkoff's position in life, and as a result, the other students begin to take notice of him as well. But that changes on field day, when Zinkoff's clumsy athleticism loses the competitions for his team. Because of this, his teammates vocally address him as "Loser" for the first time. Even though this takes a toll on his spirit, he soon recovers and is eventually back to his old self, though now more mature (he does not laugh impulsively or scream "Yahoo" as he used to). Once he is in fifth grade, Zinkoff tries to fit in more than he used to. He briefly befriends Hector Binns, but the friendship soon falls apart. He purposely avoids Field Day once it arrives so that he does not let anybody down. When he graduates elementary school, however, he knows that he will miss everything about Elementary school, the good and the bad.
As Zinkoff enters middle school, he begins to dissolve into nothingness. He is not regarded as a loser; he is regarded as nobody. He still has fun with his life, but nobody notices him anymore. Once the school year's first snow arrives, Zinkoff finds out that a toddler in his neighborhood, Claudia, has gone missing. He realizes she ran away and decides to search for her as well. Claudia gets found a few minutes later, but Zinkoff does not notice. In fact, he trudges through the snow for seven hours in search of Claudia, all the while unaware of the state of emergency being lifted soon after he began his search. Eventually, he is found, just before freezing, and is brought home. His family is glad to see him not hurt, and praise his heroic efforts.
The story ends with the other kids slowly recognizing the size of Zinkoff's heart, and, not that they understand him completely, they figure he's not so bad. Aside from some negative comments, a particular boy sees Zinkoff as just another kid (albeit one who did something heoric) and so he treats him like any other, and Zinkoff finally gets to play football with the other children.