It is very important to develope, as a part of training technologies, appropriate tools, or tests to validly and objectively control the level of specific skills development. This study aims to determine reliability and validity of the test for evaluation of specific running agility development level of young volleyball players. Male subsample consisted of 63 boys and 146 girls. Total subject sample was also divided into age categories, where boys consisted of: 29, 21 and 13, and girls: 65, 37 and 44-U15, U17, and U19 respectively. All subjects were tested using modified X test. Differences were determined with ANOVA, while reliability evaluation was performed using Reliability analysis and Aplha and ICC criteria, as well as Linear Regression Analysis. Results showed that there were significant differences between age groups for both male and female subject (p = 0.002 and p = 0.000, respectively). Test showed high reliability (>0.82) for both day-by-day and trial-by-trial models. In general, applied modified X test, proved to be statistically reliable and sensitive to observed age groups of subjects, and therefore it can be recommended for use in volleyball training technology.