August ("Auggie") Pullman (Jacob Tremblay) is 10 years old, a precocious little boy who lives in Brooklyn with his parents, older sister Olivia ("Via") (Izabela Vidovic), and dog Daisy. He was born with a rare medical facial deformity, mandibulofacial dysostosis (otherwise known as Treacher Collins Syndrome), and has undergone 27 surgeries in order to see, smell, speak and hear. Up until this point, his parents Isabel (Julia Roberts) and Nate (Owen Wilson) have home-schooled him, but it is decided that he be enrolled to attend middle school at Beecher Prep. Before starting classes, Auggie meets Principal Tushman (Mandy Patinkin) who arranges a tour for him with three other students: Jack (Noah Jupe), Julian (Bryce Gheisar), and Charlotte (Elle McKinnon). When school starts, Auggie is received with stares and jests from his classmates, leaving him to silently bear the tension. However, he soon forms a friendship with Jack and finds support through his teacher, Mr. Browne (Daveed Diggs).For Halloween, though Auggie planned to dress as Boba Fett, he settles on a Ghostface costume from the previous year and walks through school feeling optimistic since the getup allows him some anonymity. Upon entering homeroom, he sees Jack speaking to his friends Julian, Amos (Ty Consiglio), Miles (Kyle Breitkopf), and Henry (James A Hughes). Unrecognized because of his costume, Auggie is dismayed to hear them making fun of him behind his back. Among other remarks, the one that stings the most is that "[he] would kill [himself] if [he] looked like Auggie". Auggie becomes sick and his mother has to leave a mother-daughter day with Via to pick him up. Though she is hurt, Via convinces Auggie to go trick-or-treating.Auggie finds a sympathetic soul in Summer (Millie Davis) and confides in her about Jack's betrayal. Later, when Jack asks Summer why Auggie is avoiding him, she only says "Ghostface". Suddenly realizing what he's done, Jack resolves to make it up to Auggie and agrees to be partnered with him for the Science Fair, despite Julian's protests. When Julian confronts him in the hall and calls Auggie a freak, Jack hits him in the face and they fight before teachers break them up. Jack is suspended for two days and, though he refuses to give a reason for the fight in an apology letter to Principal Tushman, the principal responds saying that he thinks he understands why, and encourages Jack to keep being the good kid he knows he is. Jack then sends an apology to Auggie via Minecraft, telling him he said what he did only to gain favor with Julian's friend group, and they reconcile.Meanwhile, Via signs up for the drama club with classmate Justin (Nadji Jeter) with whom she soon begins a relationship. At that point, she realizes she cannot keep secrets from someone she cares for and admits to him that, contrary to what she initially told him, she is not an only child. She brings Justin home to meet her mother and brother. Justin treats Auggie with kindness and tells Via that he understands her hesitation to tell him about her brother. Via is selected to be her classmate Miranda's (Danielle Rose Russell) understudy in the lead role for her school's production of 'Our Town'. On opening night, however, upon learning that her family is not in attendance while Via's is, Miranda feigns illness. Via fills in for the role and gives a moving performance, earning a standing ovation.Meanwhile, Auggie's popularity and circle of friends grows throughout the year, but he is still bullied by Julian and his friends. When Mr. Browne finds Auggie holding a photograph that had been stuck to his locker, he presses him, then Amos, for information. This results in Julian and his parents being summoned to see Principal Tushman who explains the school's zero-tolerance policy on bullying. He shows Julian's parents (Yan-Kay Crystal Lowe and Steve Bacic), the photograph from which Auggie has been photoshopped out and on which the sentence "Do everyone a favor and die" is written. Julian's mother admits to photoshopping Auggie out of the picture because she wants visitors to their home to focus on her son rather than the Pullmans. She further states that her son's normal good behavior and their financial donations to the school should supersede any suspension. Principal Tushman, however, is persistent and won't abide by bribery or threats. While he accepts Julian's apology, he cannot prevent the boy's parents from deciding to place him in another school.Later, at a class trip to a nature retreat, Auggie and Jack are confronted and antagonized by a group of seventh graders. Things become heated as Jack and Auggie attempt to fight back, but Amos, Miles, and Henry appear to defend them and they all escape the seventh graders. They retreat to the edge of a lake where Auggie becomes emotional at the kindness he's received, especially by former bullies.At that year's graduation, Auggie thanks his mother for enrolling him in school. She tells him, "You really are a wonder, Auggie." He is given the Henry Ward Beecher Medal for his strength and courage throughout the school year. The movie ends with everyone cheering Auggie as he delivers a voiceover narration (quoting the last precept Mr. Browne gave in class): "Be kind, for everyone is fighting a hard battle. And if you really want to see what people are, all you have to do is look."