Final answer:
In 'Wonder', Julian is the school kid who behaves meanly towards August when showing him around school with Charlotte and Jack.
Step-by-step explanation:
In the book Wonder, the mean kid who showed August around the school with Charlotte and Jack was Julian. Julian was known to be unfriendly and unkind to August right from the start, making it clear through his actions and words. He consistently teased and bullied August, primarily because of August's facial difference, which is a central theme of the book's exploration of kindness, acceptance, and friendship.