Current research suggests that teacher development evolves in stages, and that teacher concerns as professionals are central to teacher development. The concerns theory suggests that teacher growth involves a gradual change from concerns about self, to concerns about the task at hand, to concerns about the connections and implications of self, students, and task (the impact stage). A checklist for measuring and drawing the characteristics patterns of the stages in teachers' concerns was recently presented by F. F. Fuller and G. D. Borich (1969, 1986, 1992, 1995). This Teacher's Concerns Checklist is recommended for assessing the educational needs of preservice teachers, especially in the formative evaluation of teacher education programs. In this paper, early findings from a classroom-based study of the Stages of Concerns Checklist are reported. These findings are from data collected over 3 consecutive semesters in 3 teacher education classes in 1994 and 1995 for a total of 66 students. Results support the reliability of the checklist with preservice teachers, and they support its construct validity in broad terms. Recommendations are made for additional checks of the instrument's validity against some other existing measures of teachers' stages of development and for use of larger sample sizes to enhance the instrument's potential for external validity. Appendixes contain the Stages of Concerns Checklist and frequencies for task-self-impact aspects with histograms for normality. (Contains 6 figures, 7 tables, and 31 references.) (SLD)