How does one teach number? Is there any way to apply Piaget's theory to the classroom? What activities are better than worksheets for helping children develop number concepts? Arguing that Piaget's research and theory are indeed useful to the classroom teacher and can make a major difference in how one teaches elementary number concepts, the author of this booklet focuses on how the kindergarten and preschool teacher can use Piaget's theory in a practical way, discussing the following four topics: the nature of number, objectives of teaching number, principles of teaching number, and situations in school that the teacher can use to teach number. A discussion of Piaget's theory in the area of morality and autonomy and its implications for teaching arithmetic in preschool and kindergarten is included in the appendix. (MP)