Humane education is a long-standing field of education that endeavors to nurture kindness, compassion, and concern for nonhuman animals, people, and the environment. Despite its long history, however, few randomized control studies have evaluated its effectiveness to promote the development of relevant outcomes. The current study sought to address this dearth by investigating the effects of a humane education program on not only participating students' attitudes, but also their behaviors. Classes of under-served, fourth-grade students in two major US cities were randomly assigned to participate in either a school-based humane education program or a chess club (the control group); all students participated in their respective activity during the same period once a week for 11 weeks. Data were collected on the attitudes (n = 236) and behaviors (n = 167) of participating students exactly one week before and exactly one week after these programs were conducted. Students self-reported their attitudes about the treatment of animals and the environment via the Intermediate Attitude Scale. Teachers rated each students' prosocial and disruptive behaviors through sub-scales of the Teacher Observation of Classroom Adaptation-Checklist. Nested multilevel models of change found that the development of prosocial behaviors and self-reported attitudes significantly interacted with group assignment: Students who participated in the humane education program showed stronger growth in both of these outcomes compared with students in the control group. Changes in disruptive behaviors, how-ever, were not found to differ between groups. The results support the effectiveness of a humane education program to teach a relatively large and diverse group of upper elementary students to learn about animal welfare issues and to improve their prosocial behaviors. Effects appeared strongest on attitudes; behavioral effects were found to be largely limited to behaviors directly addressed by the humane education program.