The emphasis of the teaching and learning estimation (TLE) in mathematics education is a recent common feature to Japan and USA. The purpose of this paper is to make clear the present state of TLE in USA and its fundamental conception.
By analysing four mathematics textbook series published before the "STANDARDS" (1989), all of them deal with estimation in relation to measurement, computation, and problem solving. Therefore, the intention of emphasising TLE in the "STANDARDS" is not to introduce estimation as a new topic into mathematics curriculum but to improve TLE. It is the fundamental conception of TLE to develop the individual student's estimation mind-set.