The finale of both seasons, when all the previously eliminated contestants return to take part in the final challenge somehow. What does everybody do before the final challenge? Do they make sneaky plans like they have been the whole time, or yell at one another for past betrayals and arguing? Nope. They just mess around and have fun throughout the night.
The Nerd-Off of season two with Zack and Nicole. Zack makes it clear many times that he does not want to send her home.
In the second season, the final challenge is a gauntlet of eight brain-testing challenges, such as Sudoku or Pac-Man. The final two contestants can petition to try and get previously eliminated contestants to help them out. There is only one previously eliminated contestant who needs literally no convincing whatsoever: Zack, who practically announces before even going back inside Nerdvana that he's going to help Jack.
In Episode 4 of Season 3, Colby (the Jeopardy! champion) revealed that the first thing he did with his prize winnings from the show was to buy his mother (whose purchase of an encyclopedia set kick-started his lifelong love of learning) a house in the suburbs so she could move out of the dangerous neighborhood he grew up in.