A match or mis-match of cooperating teachers and student teachers on personality characteristics may have an important role in the overall effectiveness of the student teaching experience. Among the different personality factors that may affect participant relationships are flexibility, empathy, and self-esteem. To assess the validity of measures of these traits, 63 cooperating teachers rated themselves on 3 instruments: the Self-Perception Inventory, the Rehfish Rigidity Scale, and the Empathy Construct Rating Scale. Their student teachers and university supervisors rated them on the same instruments. The convergent and discriminant validities were examined for each instrument. Of the scales used to assess the three personality factors which may influence relationships among student teaching triads, only one, the instrument intended to assess flexibility (Rehfish Rigidity Scale), showed adequate validity through the statistically rigorous multitrait-multimethod design. The results of the study emphasize the need for further methodological studies in the examination of teacher characteristics. (JD)