Inservice, preservice, and prospective teachers and nonteacher controls (N=408) participated in a cross-sectional study of the development of beliefs about use of critical-thinking (CT) activities with different learner populations. Teachers' self-selection of their careers was associated with strong support for high-CT activities for both high- and low-advantage learners. Preservice education was associated with reduced support for (a) high-CT activities for high-advantage learners and (b) low-CT activities for both learner populations. Inservice education and teaching experience were associated with slightly reduced support for high-CT activities for low-advantage learners. Preservice education seems a propitious time for promoting changes in CT-related beliefs. From the viewpoint of CT advocates, initiatives are needed to counter the apparent reductions in teachers' support for high-CT activities.