Reconciliation
To assuage her guilt for having stood by while Peggy teased Wanda, Maddie seeks to reconcile with Wanda. Her desire to restore friendly relations sends Maddie into Boggins Heights, and eventually to write Wanda a letter. However, these efforts only temporarily silence Maddie's guilt. Without a face-to-face reconciliation, Maddie will never know whether Wanda truly forgives her. The reconciliation Maddie craves is deferred until the book's final chapter, when Maddie recognizes her own features in the drawing Wanda gave her. In lieu of a face-to-face reconciliation, Maddie receives information that allows her to believe that Wanda had liked Maddie all along.
Bullying
Though the author does not use the word, the book's most prominent theme is bullying. Though Peggy is naïve in her child's perspective, the "hundred dress game" she instigates with Wanda is mean-spirited at heart. Because Wanda remains stoic and doesn't react to the schoolyard taunts by crying, Peggy and other girls can tell themselves that their actions are not cruel. In this way, the book captures the nuanced and insidious nature of bullying: from a certain perspective, it is just a game; from another, it is cruelty.
Equality
The theme of equality enters the narrative when Peggy and Maddie arrive late to class as their fellow students are reciting the Gettysburg Address. First delivered by Abraham Lincoln in 1863, the Gettysburg Address touches on the American constitutional ideal that "all men are created equal." Room 13 reads the speech in unison every morning, which is ironic, given that the speech's message of equality does not reach the girls, who treat Wanda as a lesser human. Equality becomes increasingly relevant as the story progresses and Wanda rises from her lower status to a more equal social standing within the classroom.
Class Difference
Several details about Wanda's life signal that she and her family belong to a lower social class than most of the students in Room 13: She has a Polish surname, she wears the same dress every day, her brother works at the school, her father's English is undeveloped, she lives in Boggins Heights, and she has difficulty reading aloud in class. Wanda's classmates may not realize it, but their desire to tease Wanda likely stems from an inherent bias against Wanda's lower class position.
Remorse
Remorse drives the plot of The Hundred Dresses. Maddie's guilt leads her to obsess over how she should have stood up for Wanda, and eventually sends her on a quest to reconcile with Wanda. Maddie's remorse is conveyed in the distracting thoughts she has during class, in her fantasies about protecting Wanda, in the trip she takes to Boggins Heights, and in the letter she and Peggy write to Wanda. Knowing that the book is semi-autobiographical, the reader can deduce that the author's remorse was so great that she (i.e. Maddie) eventually wrote a book about the incident.
Poverty
The theme of poverty underlies much of the conflict in The Hundred Dresses. Poverty determines that Wanda and her family live far from school, and the mud Wanda accumulates on her shoes during the long walk subsequently relegates her to the back of the classroom, where she sits with students whom the teacher and front-row students presume to be unintelligent. Wanda's poverty also means she wears the same dress to school every day, which brands her as a social outcast. Maddie's own poverty stops her from defending Wanda, because Maddie fears she herself will become a target of abuse if people found out that Maddie wears Peggy's old dresses. Ultimately, Wanda's kind heart and drawing skills prove to the class that her poverty does not indicate that she is any less worthy of praise and acceptance.
Social Isolation
Starting with the image of Wanda's empty desk at the back corner of the classroom, and ending with the recollected image of Wanda standing alone against the ivy-covered wall, the theme of social isolation pervades The Hundred Dresses. The hundred dresses "game" that Peggy "plays" with Wanda is tacitly designed to keep Wanda at a distance from the group of popular girls, with whom Wanda would like to be friends. Wanda's loner status at school mirrors her Polish family's social isolation in Boggins Heights, where the only neighbor mentioned is an old man who lives alone.