Constructivism, as a set of theories about how learners learn, has been an important discourse in the educational research literature for a number of years. Interestingly, it has been far more visible in science education research than in environmental education research. This article considers conceptual change theory within constructivism as a contested concept, outlines differing expressions of constructivism in science education and environmental education, and argues for approaches to environmental education that adopt socially constructivist perspectives with respect to the character of the subject matter content as well as to learners' apprehension of such content. In considering implications for research, this perspective is juxtaposed with a recent United States Education Act, which prescribes a far more objectivist approach to educational research and which serves as a reminder that research itself is a powerful factor in shaping how we construct the nature of subject matter, learning and the implications of these for teaching practice.