Abstract: An investigation was made among the 4th, 5th and 6th graders for the purpose of studying the relationship between 1) variations in the structure of arithmetical problems; 2) the psychological activity of the pupils and 3) their ways of formulation of the problems. The results showed a complex relationship with the same kind of formulation of problem structure caused by different kinds of psychological activity; and with the same kind of psychological activity resulting in different ways of formulation, especially when the structure of the problem was in conflict with the maturity level of the pupils and also their habitual ways of mental activity in problem solving.

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