The purpose of the present study was to examine: a. the development of primary school students' motor coordination (MC) within three years, b. gender as a crucial factor of this development, c. the relationship between MC and Body Mass Index (BMI). Students' performances as well as the BMI of 20 boys and 22 girls were measured throughout a three-year period. Students' MC was evaluated with Körperkoordination Test für Kinder (KTK) a test with four subtests in order to evaluate Motor Coordination (MC) of 5-14-year-old children. Results indicated that: a. the MC increased during the two first years of program b. that there was a negative correlation between BMI and KTK results/every year: Increases in BMI were correlated with decreases in a rating of KTK results/every year c. there was a statistically significant interaction between motor coordination and BMS. From the analysis of the results and the discussion that followed we came to the following conclusions: a. the participation in organized physical activities could help students who were at the first and second class to improve-develop their motor coordination, b. the increase in body mass index had a negative impact on the size of children's knee joints, c. the body mass index can successfully predict the extent of the knee joint and the gender of the boys contributed to this prediction.