The socially constructed beliefs that teachers hold about knowing, teaching, learning, and praxis are likely to have a profound influence on their practice. Too often teachers serve to reproduce traditional authoritarian and didactic patterns of instruction in schools, apparently because they themselves have never been given the opportunity to conceive of education as a project of possibility in which students engage in the critical and social construction of meaning. Examination of research literature suggests that most teachers believe teaching to be a didactic, authoritarian activity, and that in their teaching they appear to teach in a manner quite consistent with this belief system. A systematic theory of teacher cognition is needed to validate an alternative to the existing behavioristic and didactic approach to the education of teachers. This paper raises the possibility that developmental psychology, specifically the study of adult intellectual development, may be well equipped to fill the void by conceptualizing and investigating the issue of teachers' beliefs, and their relation to practice, from a cognitive-developmental perspective. A preliminary research agenda for constructivist investigation of teachers' beliefs is proposed. (IAH)