ENThe objective of the analysis presented in the article is the change in the classification thought operation in the seventh year of a child's life. The analysis was made from two aspects: the social aspect -how social-demographic characteristics are related to the development of the classification operation, and the educational one - how different training methods influence the development of this thought operation. On the basis of integrated analyses of these two aspects it can be stated that systematic and relevantly prepared pre-school education could be beneficial to the child's cognitive development and further investigations to determine what kind of environment is unfavourable to a child's development are necessary to be carried out. [From the publication]