Lyddie and Bridge to Terabithia share many common themes, as do most of Katherine Patterson's books. Both are coming of age novels, where the protagonists must overcome obstacles both outside themselves and within their own characters in achieving maturity. For Lyddie, it is stubborn pride that she must reconcile. Fiercely independent, she faces responsibilities far beyond what she should have to deal with at her age, keeping her family together and fed when her father leaves and her mother sinks towards madness, yet she makes her situation even more difficult than it needs to be by refusing the help of those, like Mr. Stevens, who would come to her aid. For Jesse, the protagonist in Bridge to Terabithia, it is his tendency to be afraid that her must come to terms with. Through his friendship with Leslie, and her unconditional acceptance of him, he develops self-confidence and learns to work around his tendency to be reticent.
Family is another theme common to both books. Both Lyddie and Jess explicitly express their devotion to family through their treatment of their little sisters. Lyddie takes responsibility for her sister Rachel after her mother's death, and Jess resolves to nurture his sister Maybelle after Leslie is killed in the river.
A third common theme to the two books is the importance of books. Lyddie, who is barely literate, derives comfort and strength from nightly readings of Oliver Twist as rendered by her friend Betsy, and Jess finds a refuge in the imaginary world based on The Chronicles of Narnia created by Leslie.
Setting plays an important part in both stories. Both Lyddie and Jess live in rural environments in the eastern United Stattes, and both are profoundly affected by the times in which they live. Lyddie must deal with the restrictions placed upon women in the mid-1800s, and she experiences firsthand the horrific conditions women faced as part of the workforce in a newly industrial society. Jess, who lives in the turbulent 1960s, must reconcile the changing value systems presented by the hippie culture as represented by his music teacher and the Burke family as it clashes with the Christian but materialistic culture of his own family.
Both novels are narrated by the main characters, Lyddie and Jess, in a straightforward, honest style. Through the telling of their stories, the reader is given a sense of both the details of the narration, and the inner thoughts, impressions, and feelings of the protagonists.