Mathematical computation consists of both written computation and mental computation. The strategies for mental computation can be used to check the reasonableness of written computations. Mental computation has two distinguishing characteristics: "it produces an exact answer, and the procedure is performed mentally, without using external devices such as pencil and paper" (Reys, 1984, p. 548). It is important to consider the accuracy and efficiency of various mental computation strategies and this can be useful to discuss with students. Discussion about different strategies will enable students to consider different approaches and work towards development of efficient mental strategies for computation. Utilising a variety of strategies and methods for computation will enable students to develop a better understanding of computation processes and number sense. In this article, the authors put forth a strong case for an emphasis on developing mental calculation strategies with students, and suggest helpful teaching approaches to achieve this. (Contains 4 figures and 2 resources.)