A goal of most environmental education is to motivate students toward environmentally friendly behaviour change. This article describes a study that elucidates how such motivation can be fostered in the classroom. It compared students' development of environmental motivation in a conventional post-secondary environmental biology course and a similar course guided by self-determination theory (SDT). Students in the SDT-guided course experienced less amotivation after the course than students in the comparison section. This article presents a preliminary empirical examination of the utility of SDT in a formal environmental education setting. (Contains 1 figure and 3 tables.)