Figure 1.

Eduball set. Balls used in the experiment were divided into two main subcategories. (a) The first type of balls (57 cm in circumference and 310 g of weight; close to size 3 basketballs) are in yellow and green colors (40 in each color) on which are printed black letters (on one side uppercase and on the opposite side lowercase) and numbers (from 0 to 9; the same digit on the top and bottom side); (b) the second type of balls (63 cm in circumference and 250 g of weight; close to size 4 volleyballs) are in blue and red colors (eight in each color) on the surfaces of which mathematical symbols are painted (representing the operations of addition, subtraction, multiplication, division, the symbols of greater than, less than, and parentheses), including the “at” sign (@), as well as four unprinted orange balls that can be used as universal blanks.