In the article, on the basis of the analysis of psychological and pedagogical sources the concept of computing activity, its structure and functional parts are defined. For this, the following methods of research were applied: theoretical – analysis, classification and synthesis of scientific literature for comparison and contrast of different approaches to the problem and disclosure undertaken to definitions presented in the publication and empirical – observation of computing activity of students. As a result of the analysis of psychological sources, the structure of activity is determined. We consider mental actions as meaningful structural elements of mental activity to which the computing activity belongs, and the quality of mental action formation depends on the quality of orienteering activity based on orienteering action. The functional parts of computing activity are singled out: orienteering, executive and control-correctional. The orienteering part is central and lies in the particular case of correlation between calculations known to pupil and computational techniques and ways of reasoning, ascertaining their possible application in this particular case, the approval of one of them, and actualization of the orienteering bases of action. The executive part of the computing activity involves the implementation of one of the computational techniques or ways of reasoning, and the control-correction part, further evaluating the rationality of the chosen path and the possible use of another technique or way of reasoning. It has been established that fast and correct calculations are related to the ability of the pupil to actualize the required computation, which is more effective than other techniques as it leads to the result and the ability to quickly and unmistakably implement the operations that make up this technique. Since the need for computing occurs to a person at all times, then the motives of computing activity arise on the basis of practical needs, the satisfaction of which implements its purpose – to find the result of the arithmetical actions of addition, subtraction, multiplication and division (complete or with the remainder) in the set of integer non-negative numbers. In the future, we see the need to investigate the problem of computing.