Abstract: The experiment was conducted to study the development of the mental representation and processes underlying the knowledge of conventional time 20 primary school pupils from each of grades 1 , 3, 5 , and 20 university students served as subjects. they were asked to judge whether or not a given day of the week was one of the next 3 days after the reference day. The results Showed that, (1 ) The scores of cognitive processes underlying performance on the tasks of conventional time increased with age. (2) the distance effect and the boundary effect were both significant. The response time and the number of errors increased with the increasing of the distances between the two days, the longest response time and the greatest number , of errors ocurred adjacent to the category boundary (3 days after the first day). (3) The Subjects could use number, to solve the problems of conven- tional time, 1 and 3 graders solved the problems by means of counting recitation, some 5 graders could use image processing to judge the task, most of the 20 year old subjects solved the problems by means of calculation of numbers and image processing.

Key words: conventional time, cognitive process, model representation