The objective of the present study was to evaluate the level of the physical development and health of the children and adolescents depending on the age and sex using the methods and principles of pathophysiological investigations. The study involved 15,067 Moscow-based schoolchildren at the age varying from 7 to 17 years, including 7,760 boys and 7,307 girls. It was shown that the girls aged 7-14 and boys 8-16 years had body mass index (BMI) significantly different from the respective normal-for-age values. The boys aged 8 years or more had a significantly higher BMI than the girls of the same age which suggests a greater prevalence of the hypersthenic body type among the boys of this age group. The most intensive growth of body mass index was observed in both the girls and the boys during the period between 8 and 9 years. It is concluded that BMI in addition to gender and age is a major factor influencing the health status of the schoolchildren. The children and adolescents having the normal body type were characterized by a higher physical health index (PHI) in comparison to those with hypo- or hypersthenic body type. The index of physical health sharply decreased in both the boys and the girls within the first school year. A rise in the index of physical health was observed in the girls starting from the age of 14 years and in the boys from the age of 13 years. By the age of 17 years, the boys had a higher index of physical health in comparison with that in the girls. By the time of graduation from school, the index of physical health was lower regardless of gender than it was at the entry to school.