Traditional approaches to bullying intervention focus on the bully-victim dyad. However, research indicates that bullying is a group phenomenon and often occurs in the presence of peer witnesses. Bystanders are uniquely situated to either deter or facilitate the social power play that can underlie bullying behavior. Specifically, individuals who bully others may be motivated by a desire to gain (or maintain) high status among their peers. Bystander-based bullying interventions are able to exploit this by directly targeting social components that reward and maintain bullying behavior, such as peer support of bullying, thereby disrupting the social feedback cycle involved in perpetration. However, bystander-based bullying interventions for elementary students pose a unique set of challenges in terms of fostering the awareness of bullying, social thinking, and cognitive-emotional skills that are necessary for positive bystander action. Children’s literature is a promising medium to facilitate elementary-aged students’ access to social-emotional knowledge, skills, and behavioral change. This study sought to add to the theoretical research base of bystander behavior using a majority-Hispanic sample to investigate the relationships between several theoretically-linked bystander-related variables and determine predictors of positive bystander behavior. Secondly, this study investigated the effectiveness of a literature-based, bystander-targeted, bullying intervention (the Bullying Literature Project) on children’s bystander behavior, attitudes towards bullying, prosocial behaviors, peer friendships, and victimization. Finally, potential moderators of the intervention on bystander behavior were investigated. Results revealed differences across grade and gender for select variables of interest, identified anti-bullying attitudes and victimization as significant predictors of positive bystander behavior, and identified a small, negative correlation between peer friendship and victimization, among other significant correlations. Main results revealed the Bullying Literature Project increased positive bystander behavior (small effect size) and teacher-rated prosocial behavior (large effect size), compared to the wait-list-control group, in a subset of the dataset. No moderation effects involving gender, peer friendship, or anti-bullying attitudes were found. Discussion and future directions of bystander-based bullying interventions are reviewed.