In order to help preschool children understand mathematical principles, five different learning activities designed to help them think about physical transformation or change are described. Introductory remarks focus on Piaget's concept of transformation and on various strategies teachers can use to help children consider changes in the state of an object. Suggested strategies include preparing the environment with a variety of materials, parallel play, modelling, questioning, and conflict inducement. The specific learning activities discussed are sand play, play dough, shadows, painting, and the use of a silhouette sorter (a sorting box with holes of various shapes cut from its surface into which children can place corresponding blocks). (RH)