The plot of Wonder revolves around the life of August "Auggie" Pullman, who was born with a facial condition that led to him being educated at home through the fourth grade. He begins fifth grade at Beecher Prep, where he is bullied at the hands of many of his classmates—particularly by a boy named Julian Albans. Auggie makes two friends at school, Jack and Summer, and somewhat settles into the year until an incident on Halloween in which he overhears Jack make fun of him to Julian and several others. August's older sister, Via, feels largely ignored by her family and struggles socially in the new school year since she is no longer on speaking terms with Miranda and Ella, her two former best friends.
Auggie and Jack become friends again after Jack punches Julian to defend Auggie's honor. Auggie is devastated when the Pullman family's dog, Daisy, dies suddenly, which is coupled with hurt at realizing that Via does not want him to attend her school play and cause unwanted attention. Via and Miranda become friends again after Miranda fakes sickness so that Via can assume the starring role in the play. When Auggie is attacked by older boys on an overnight school retreat at the end of the year, three classmates who typically bully him come to his rescue, at which point he begins to feel accepted and school life becomes more tolerable.
At the end of the novel, Auggie wins a special award at school and learns that Julian will not attend Beecher Prep next year. He is also thrilled when the Pullman family gets a new puppy. Auggie has learned not only to navigate the everyday details of attending school, he has also formed meaningful friendships and gained confidence in his identity. The novel concludes with his mother proudly telling him that he is a "wonder."