The longitudinal survey of schoolchildren's physical development was undertaken for 4 years with the 6-month interval. The schoolchildren of the 4th-7th grades were examined compared to swimmers of the same age (30 boys and 30 girls, 120 children all together). As a result nonuniform increase of growth and weight indicators, those of breast circumference and excursion, vital capacity and hand strength was established. The indicators' increase depended on age, sex, regime of motor activity and time of the year. because of girls' earlier puberty by the age of 12 they went ahead of boys by anthropometric indicators but by the age of 14 boys were again ahead of girls by all the indicators of their physical development. The highest growth of all morphologic indicators in sportsmen and others was established during the period from April till October, i.e., in spring and in summer. Regular swimming lessons promoted not only better physical but also harmonious development of adolescents. At the same time relatively early specialization in swimming hindered girls' puberty, especially at the age of 13. Thus it was necessary to set standards for physical load and to assess body functional capacity taking account not only of actual but also biological age.