Purpose. The aim of this study was to examine the process of how motor skills were developed and shaped in boys and girls in relation to their rate of maturation, based on the use of peak height velocity (PHV), which measures biological maturity. Methods. This study made use of a longitudinal study researching the physical fitness of boys and girls from Kraków, Poland during the years 1980-1990. From the original sample population, 296 boys and 196 girls were selected for further analysis. Physical fitness tests were administered over the subsequent decade, measuring the following motor skills: speed, explosive strength of the lower limbs, static strength of the right and left hand, agility, dynamic strength of the abdominal muscles, static endurance of the upper limbs and shoulders, and flexibility. On the basis of the median and PHV age quartiles for both sexes, the examined individuals were divided into two cohorts: early maturers and late maturers. The mean values and standard deviations of the physical fitness test results were calculated based on biological age. Afterwards, the means and standard deviations of each tested motor skill of the early maturers were standardized into means and standard deviations of the late maturers. Results. The motor skills best performed in all age groups and in both sexes by early maturers were in tests of static strength of the hands. In the group of boys, early maturers in all age groups also performed the best in tests of speed and explosive strength of the lower limbs. Late-maturing girls were positively differentiated in each age group in tests of static strength of the upper limbs and shoulders, and in the dynamic strength of the abdominal muscles. Conclusions. The rate of maturation was found to significantly influence the results of fitness tests, particularly in the case of boys.