This study, which is part of a complex research carried out by educationists, physicians and psychologists, evaluates the results of five years’ longitudinal study of the development of physical efficiency of children from 6 to 11 years of age. Its aim was to find out how children develop under various conditions of the school P. T. practice conducted according to valid pedagogical norms and thus obtain more objective data for the modernization of P. T. courses. It is one of the items of the study of physical efficiency of the pupils concerned, a starting point for judging the relationships between their physical development, psychical development and physical efficiency. The development of the children was followed in a complex manner in six classes from the 1st to the 5 th year of the Basic School in larger towns in the period from 1980/1 to 1964/5. The research was concerned with the conditions and the level of P. T. and its specificness at individual schools. Physical efficiency of the children (50 metres race, long jump, high jump, throwing a ball and full bend) was uniformly tested twice a year. On the basis of statistical characteristics of the pupils’ performances and using the technique worked out by Merhautovd — Reisenauer the reserchers arrived at a mathematical model for the evaluation of the signs of children’s physical efficiency, at a summary index of the pupils’ physical efficiency from the viewpoint of the level and synchronism. They evaluated the development of the physical efficiency of each pupil, groups of boys and girls, each class and its specificness. The data thus obtained were confronted with pieces of knowledge about the volume and quality of the P. T. process in the respective classes. In this way certain information was obtained about the influence of the P. T. process and its individual factors on the physical efficiency of the children among whom the research was carried out, some suggestions were made for modernizing P. T. courses for junior pupils from the viewpoint of its purpose, system, content and methods of work.