This ethnographic study at a public high school in the Northeastern United States investigates the process of change in students’ environmental identity and proenvironmental behaviors during an Environmental Science course. The study explores how sociocultural factors, such as students’ background, social interactions, and classroom structures, impact the environmental identity and behavior of students. In this investigation, the identity theory of emotion of Stryker (2004) from the field of sociology is utilized in the interpretation of students’ reactions to classroom experiences as they proceed through the Environmental Science course. The participants in this study are an Environmental Science teacher and the 10–12th grade students in her Environmental Science elective course. The researcher collected data for a period of six months, attending class on a daily basis. Data was collected through participant observation, videotaping, interviews, and cogenerative dialogues. The results of this study inform science educators by illuminating important elements, such as students’ emotional responses to activities in class, conflicting elements of students’ identities, and students’ openness and willingness to critically reflect upon new information, which contribute to whether a student is likely to change their views towards the environment and pro-environmental behaviors.