1985'3, p.49
Zak A. Z.
Relation between learning and mental development in schoolchildren

Ability to do mental operations has been studied in I-X form schoolchildren as a function of the content of mathematics as a school subject. The study was based on the author's concept of thinking as a two-dimensional three-level process; the above ability has been treated therefore as a necessary factor in the search for a solution mediated in its turn by the ability to operate with images and semiotic substitutes of problem's conditions. The author's experimental technique (1983) has been used. It is concluded in the article that the second level of development of the considered ability corresponds to the acquisition of four arithmetical rules of dealing with natural numbers within a hundred, while appearance of the third level correlates with acquisition of the whole course of arithmetics.