Abstract
Process-product research on teaching, an adaptation of the criteria-of-effectiveness paradigm, has its roots in functionalist psychology. Functionalism is a pragmatic and eclectic approach to psychology that is concerned with the fitting of persons to environments. Functionalists have always accepted cognitive behavior as a legitimate object of study. Thus, a perspective from functionalist psychology may be useful for designing studies of teachers' thinking. From this perspective, the majority of contemporary studies of teachers' thinking are found wanting because there has been no concern for criteria of effectiveness. Recommendations for the improvement of research on teachers' thinking are offered.