Tanner scores of pubertal development were determined in 194 girls and 190 boys of the fifth and sixth grades. There was a wide scatter of Tanner scores both within and between sexes, reflecting considerable variability of pubertal development in these age cohorts. Physical performance depends on muscle mass and muscle strength. Since these variables are related to pubertal development, training programs and training goals must take the stage of pubertal development into consideration. A comparison of Tanner scores and sport ratings showed that the factor "pubertal development" is usually accounted for in daily practice.