A twenty-four item inventory was constructed and standardized in order to develop an instrument which measures the degree to which a preschool teacher adheres to Piaget's epistemological belief system. Using two criterion groups of teachers and graduate students--one Piagetian and one behaviorist--the inventory exhibited the ability to discriminate between Piagetians and non-Piagetians. Furthermore, a high degree of internal consistency was evidenced. The rating scale, entitled the Pre-School Teachers' Beliefs Inventory, is appended. (RD)