He appears to be the older of the two siblings, and is the more outgoing one, curious of what life was like outside their home and eager to explore the public school, wanting to see what other boys were like.
Though he is incredibly intelligent, he was also naive in a few ways; seeming astonished that "friends" would call each other names and fight, that the boys seemed to "like, yet hate" Pip at the same time, and how the other boys laughed at Kyle for liking Rebecca. Though he was continuously bullied by the others and found himself duct-taped to a bench, he was unconcerned and grew more curious each time.
Despite his parents' objections, he remained eager to explore the outside world and ultimately gave a speech explaining why it was all right for him to stay in public school.
He seems quite protective of his sister, beating Kyle up after seeing what he had inadvertently turned her into, which the other boys then considered him to be "badass" for it.
By the end of his debut, he was finding his way into fitting in with the other boys, calling Stan a "gaywad" in response to being called "nerdo".
- "家庭与社会" - Mark and Rebecca win the spelling bee. Mark is intrigued by other kids and wants to join public school.
- "混沌教授现身" - Mark is one of the contenders to replace Butters, but doesn't make the cut past the first elimination round.
- "亡命宽容营" - Mark is seen at the camp when the boys first arrive.
- "失恋的斯坦" - Seen in Raisins from the back.
- "自负警告！" - Mark is seen at party.
- "幻想大陆·上" - Mark appears at Cartman's party.