Estimation techniques for arithmetic: Everyday math and mathematics instruction

Recent advances in the way that adults perform computation in our society require reconsideration of the assumptions underlying current elementary mathematics instruction. The widespread use of calculators and computers for situations requiring precise calculation removes much of the motivation for teaching the current addition, subtraction, multiplication, and division algorithms. Yet precisely this use of computing technology now puts a premium on the exercise of estimation techniques for verifying the reasonableness of computations. These techniques, especially those that can be used “mentally” (without the use of any external tools), have been used informally for years, but never formalized for instruction. This paper discusses a range of estimation techniques, and presents in detail a series of mental estimation procedures based on the concepts of measurement and real numbers rather than on counting and integers. A set of techniques for teaching these procedures is described. These estimation techniques are evaluated against the multiple functions that elementary mathematics instruction needs to serve.