Purpose:
The paper is dedicated to the problem of testing physical capacity in primary school with the use of the Ruffier-Dickson test. The research aimed to verify the Dickson index corrected for the children’s age with the intention of usage in primary school physical education.

Methods:
Four groups of healthy males – aged 6, 7, 8, and 18 years – were randomly selected, 30 participants in each. One way ANOVA, t-test for independent samples, and intra-correlation coefficient were used to evaluate the validity of the Dickson index for the original and age-corrected functions. It was assumed that Dickson index values should not depend upon age among healthy participants in normal physical capacity.

Results:
Invalidity of the original Dickson index for 6–8-year-old children was shown, with a significant difference of their results from those of the adults (p < 0.001). The use of the index formula corrected for the age of children gives no significant difference between all the groups (p = 0.817) and a good level of validity, taking into consideration the corresponding intraclass correlation coefficient of 0.688. This conclusion is supported with t-test results (p = 0.915), which show a rather good level of the test validity.

Conclusions:
To guarantee the validity of the Dickson index, the results of heart rate measurements should be reduced proportionally to the ratio of a normal heart rate of the young patients’ population to the normal heart rate in adults.