This study investigates how the enactment of a climate change curriculum supports students' development of critical science agency, which includes students developing deep understandings of science concepts and the ability to take action at the individual and community levels. We examined the impact of a four to six week urban ecology curriculum on students from three different urban high schools in the USA. Data collection included pre and posttest written assessments from all students (n = 75) and pre and post interviews from focal students (n = 22) to examine how students' conceptual understandings, beliefs and environmental actions changed. Our analyses showed that at the beginning of the curriculum, the majority of students believed that climate change was occurring; yet, they had limited conceptual understandings about climate change and were engaged in limited environmental actions. By the end of the curriculum, students had a significant increase in their understanding of climate change and the majority of students reported they were now engaged in actions to limit their personal impact on climate change. These findings suggest that believing a scientific theory (e.g. climate change) is not sufficient for critical science agency; rather, conceptual understandings and understandings of personal actions impact students' choices. We recommend that future climate change curriculum focus on supporting students' development of critical science agency by addressing common student misconceptions and by focusing on how students' actions can have significant impacts on the environment.