The boys surprise their mom with a cruise vacation, but Carey soon discovers that they booked her as a singer in the ship's lounge; London, Maddie and Mr. Moseby try to raise money for the homeless by conducting a 24-hour Web-show marathon.
The twins persuade a sophisticated guy (Jaden Smith) to help them impress their respective dates by cooking a gourmet meal and performing a Japanese tea ceremony; Maddie finds a cell phone and becomes convinced that the unknown owner is her perfect match.
A new violinist joins the school orchestra and promptly begins flirting with Cody's girlfriend, sending Cody into a fit of jealousy. Elsewhere, London tries to learn the ropes of the hotel business by shadowing---and frustrating---Tipton employees.
Maddie returns from a trip to Antarctica, and Nia refuses to give Maddie her old shift back; Moseby schedules a team-building seminar for the Tipton staff; Zack books an entomology convention at the hotel and accidentally knocks over some crates, releasing hundreds of bugs throughout the hotel.
Zack tries to negotiate a better contract for his mom as the Tipton's nightly singer; London loses her science tutor so she asks Cody to help her with a project, but Nia also wants his help and she tries to bribe him with concert tickets.
Cody is offered a summer job at a local mini-mart if he will set up the manager on a date with London. Meanwhile, Zack discovers he's the smartest student in his summer-school class, but the other kids make fun of him.
The third season begins with Zack and Cody preparing to graduate from middle school. Unfortunately, Zack learns he failed English and won't receive a diploma until he passes summer school, but he refuses to tell his parents. Meanwhile, Maddie agrees to be a camp counselor but she's shocked when she meets the girls she is to oversee.