The article deals with scientific and applied topicality of studying the problem of children and youth social activity. Spheres of social activity display in European tradition, in particular, the European Charter, Great Britain, have been revealed. Comparative analysis of understanding the essence of such a phenomenon in Western theories and scientific pedagogical thought in Russia has been given. The changes occurred in the context of the analysis of the notion during last decades and connected with the development of volunteering, motivation and forms of youth services have been emphasized. The most important tasks in developing social activity of Russian youth have been stated. Different scientific approaches to studying the notion of "social activity" enriching its characteristics have been analyzed. Based on the analysis of results on the organized events the drawbacks, neglects and causes of poor quality of working on the development of youth social activity have been shown. The experience in choosing activities and technologies demonstrated by teachers and pupils from different regions of Russia has been presented. Theoretical analysis of foreign and domestic experience in education has enabled to offer suggestions for the expansion of pupils and students' social activity in the frame of different models presenting a wide scope for mastering and developing social competency of children and youth. These models have become the foundation for creating a general algorithm for the expansion of children and youth social activity. Pedagogical conditions and perspective directions for solving the problem of social activity development have been outlined in the article.