This paper proposes a method for teaching number applying the conservation theory of Piaget in the classroom. It is suggested that number facts cannot be taught by social transmission, since there is a fundamental distinction between logico-mathematical and social knowledge. Conservation cannot be taught to non-conservers, but there are ways to utilize and guide children's natural interest in number. Workbook exercises, math time and cuisenaire rods are not among these. Recommended teaching techniques include: (1) teach number concepts when they are useful and meaningful to a child, when the child feels a need and interest in number arising out of his daily activities; (2) use language that illustrates logical quantification or the comparison of groups (i.e., "Bring enough straws for all the children"); (3) encourage children to verify an answer among themselves; (4) encourage children to make sets with movable objects; (5) figure out how children are thinking; and (6) encourage children in a general way to put all kinds of objects, events, and actions into relationships. Snack time, distribution of materials, group games, etc. can be utilized in the teaching of elementary number concepts. (MS)