Two studies examined the effects of using a formal assessment instrument on preschool teachers' beliefs concerning the importance of various developmental skills and abilities. In Study 1, users of a formal assessment instrument rated skills and abilities assessed by the instrument as more important for preschoolers to develop than non-users. In Study 2, teachers who newly adopted the instrument rated skills and abilities assessed by it as more important after using the instrument for several months than they did prior to use, while non-users showed no change in their ratings of the same skills and abilities over time. The results indicate that using a formal assessment instrument can change teachers' beliefs concerning which skills and abilities are important for children to learn.