A statistically significant difference was found in the post test level for the regulation/behavioral variability function (Mann–Whitney’s U= .00,p< .001). In this case, Cohen’s ‘d’was not a valid estimator using the untransformed output from the
experimental and control groups, due to a zero appearing in the denominator, as a result of the SD values. Besides, by means of the graphs one can easily appreciate the small variations in the control group’s mean scores on the regulation/behavioral variability function (Fig. 6).