This study explores the influence of cognitive (knowledge and certainty) and psychosocial (social norms and efficacy) variables on youth's climate change-related behaviour, with the aim to create an empirically supported theoretical model for youth's choice to take action to mitigate climate change. This survey-based research was conducted with 453 middle and high school students within a large urban area of the western United States. Through structural equation modelling, it was found that knowledge about climate change causes and effects was a weak predictor of behaviour. Whereas social norms accepting of climate change, and the paths from social norms via efficacy and certainty, were strong predictors of behaviour. Certainty of human attribution and efficacy were rather weak predictors, mediating the influence of knowledge and norms. Students' grade level, participation in clubs and number of science classes primarily affected knowledge and social norms. An implication of this study is that if action-taking is an intended outcome of climate change education efforts, then the learning activities should address efficacy and social norms.