Introduction. The importance of socio-economic factors in differentiating the physical activities of children and teenagers keeps changing. That is why the goal of this research was to identify certain social variables amongst those listed most often which differentiate the level of targeted physical activity of urban children and youths from the Bialskie district. Material and methods. The research was conducted on 1.084 students between the ages of 10 and 18. Three age groups were chosen: 10 to 12, 13 to 15, and 16 to 18. Information about the attendance of respondents in Physical Education classes and structured extra-curricular sport activities, as well as preferred forms of physical activities were collected via a diagnostic survey. The same method was used in the assessment of the socio-economic status of the families of the respondents. The relations between attendance in extra-curricular sports activities and socio-economic factors was assessed by a multifactoral logistic regression model, and the statistical relevance of the differences was calculated by the Wald test. Results. Attendance in structured extra-curricular physical activity depended mostly on income per family member. In the case of type of work performed by parents, the attendance rate in both boys and girls was higher if the parents performed intellectual work. Parents' education and number of children in the family did not have a high influence on the attendance of respondents in structured extra-curricular sport activities. Conclusions. Increasing disproportions in societal prosperity can be an important factor limiting the attendance of the poorest group of children and youths in structured physical activities. The lack of influence on physical activity of such socio-economic variables as parents' education and the number of children in the family can be connected with the change of meaning of those factors in modern society (depreciation of the importance of higher education, decreased fertility).