Diane and Jack are the Johnson family's twins, 8 years old in the first episode and now currently 11. Young Jack is more of the sensitive type and seems to idolize his dad. He is quick to give his father a compliment, even if it does come out a little awkward.
Jack is correctly labeled as “innocent” in the series. He is sweet, kind, naive, and soft. However, he is easily manipulated by Zoey (quite rarely), Diane, and Junior though the latter is as easily manipulated as him. Jack serves as the comic relief in the family. Sometimes Jack acts silly, if not outright stupid. He comes up with ideas that are nearly impossible to carry out and lacks the typical intelligence for a boy his age. He is not very smart, in fact usually gets all D’s on tests and report cards. It takes him a lot of time to understand simple things, and calls his mistakes cute. However, quite rarely on occasion, Jack works up the nerve to stand up for himself before the people who put him down, namely Junior and Diane (but rarely the latter). But he prides himself on his dancing and basketball skills. His nickname, “Party Time”, a play on his great ability at dancing, gives him some self-confidence.