A large percent of a child's time in mathematics is spent working in the whole number system.  Operations, properties, and basic facts become crucial in the child's instruction.  In many textbooks, children are taught whole number systems and fact strategies in the following order: addition, subtraction, multiplication and division.  To follow the NCTM Curriculum and Evaluation Standards (NCTM, 1989), all four operations should be taught and developed within the elementary grades.  The importance of number sense had been referred to the "backbone" of mathematics.

As students develop concepts and explore problem situations involving operations, the teacher should provide experiences to develop "operation sense" (NCTM, 1989).  The NCTM Curriculum and Evaluation Standards define this term as understanding properties and relationships for each operation, developing relationships among operations, and acquiring intuition about the effects of operating on a pair of numbers, such as increasing addends, removing addends, skip counting, and finding missing factors. (Hatfield, Edwards & Bitter, 1997).