The notion that actions have consequences is the central theme of Whirligig. This idea is reiterated as Brent travels across the country to honor the request of Lea Zamora's mother. Positive outcomes emerge from the placement of the whirligigs, just as negative outcomes resulted from Brent's reckless driving.

Another prominent theme is isolation. Teenagers often feel disconnected from their peers, whether for real or imagined reasons. Brent experiences isolation due to frequent relocations, always being the new kid. He seeks ways to blend in and avoid standing out. However, his attempts to fit in lead to humiliation, a feeling no one, especially teens, wants to endure. Through his interactions with various travelers and the new perspectives they offer, Brent overcomes his sense of isolation and no longer feels the need to be part of the "in crowd."

Brent's physical journey mirrors his internal journey of overcoming loss, fear, and guilt—emotions common to everyone. He prepared himself for the potential loss of freedom if sentenced to jail by the judge. He feared being different and not fitting in but eventually learned that uniqueness is valuable. He experienced immense guilt and felt the need to atone for his actions. Guilt is a significant emotion that teens might face and struggle to manage. Brent seeks to alleviate his guilt through confession, apology, and atonement, setting a good example for others. Through his travels, he finds peace and forgiveness, learning how to cope with guilt.

Sixteen-year-old Brent Bishop, the protagonist, is a junior in high school. Initially, he is a self-centered young man who feels disconnected from his peers. Being the new kid in class, he feels inadequate and inferior. He believes he knows how to "fit in" this time, thinking he has the right clothes, look, house, car, and money. However, compared to the kids at Montfort, he suddenly feels much poorer. By the end of Whirligig, readers see a transformed young man, still sixteen but much more likable.

Parents and high school friends are depicted as superficial characters, serving as background figures to the plot, along with several individuals Brent meets during his journey around the country.

In alternating chapters, individual protagonists share their own stories about encountering the whirligigs that Brent constructed and installed, highlighting the positive consequences of his actions.