The article is divided into two basic parts. The first part deals with the fundamental thesis that learning represents children’s work, that this work contains general features of human work according to biological, historical and social indices. Viewpoints are given of the hygienic and physiological evaluation of changes in the pupils’ classroom efficiency. The indices of changes in the activities of the individual formations of the central nervous system are regarded as the measure of physiological conditions for the mental activity of this system. Attention is drawn to the possibilities of distorting information coded into the excitation activity by the action of a noise on nerve links. As a very significant factor influencing the efficiency of the central nervous system is regarded the conditional effect of regulation circles on non-specific formations of this system. The functional state of the cortex is influenced through the intermediary of these formations, which has a close connection with the degree of concentrated attention of the children. Then the possibilities of applying external factors in forming the efficiency of the central nervous system of children are dealt with. The time factor is functioning on the one hand as a modulator of the cyclical fluctuation of efficiency, on the other hand as a factor co-determining the size of the burden in the children’s work. The static exertion of children resulting from the position they are forced to be in while they work is functioning as a negative conditional factor. Changes in the microclimate of the classroom may have both stimulating and inhibitory influence. Stress is laid on the factor of burden, fatigue and rest limiting the efficiency of the central formations, especially in a conditional form. The second part of the article gives the results of a research into the dependence of children’s efficiency in classroom work on external factors. A deterioration in the microclimate of the classroom resulted in a marked deterioration in the efficiency of the pupils in their classroom work. One half of the windows being open twice for five minutes during the teaching period to air the classroom resulted in the microclimatic conditions being adequately adjusted, so that in the last teaching periods there was not an excessive decline in the pupils’ efficiency. When the children are in the unaired corridors during the breaks, the microclimate of the corridor deteriorates so rapidly that the effect of the children’s relaxation loses its value. The children’s stay outdoors means a definitely stimulating factor and enhances the effect of the break with the result of improving functional conditions for the psychic work of the children. We attach considerable importance to the content and length of the afternoon rest period. The required effect of the relaxation period made itself felt when it lasted until 3.30 p. m. at least, i. e. the time of a spontaneous rise in the children’s efficiency, and when the relaxation was coupled with outdoor physical exercise. If the relaxation period was cut by as little as half an hour, the functional restitution of the children was incomplete. Afternoon schoolwork resulted in a considerable deterioration of the functional indices of the children’s efficiency and the creation of pre-requisites for their overburdening. As regards the formation of the efficiency, the restitution of the functional capacity of the children is as important as the appropriateness of the burden of classroom work itself.