Sport is often put forward as a promising instrument for reaching a wide array of policy objectives. Social inclusion is one of the goals frequently mentioned. Though one can argue about the feasibility of the many claims made, sport can only reasonably be expected to play a role if the targeted population is effectively taking part in sports. This is what is investigated in this study. The focus lies on the sports participation of children and adolescents, more particularly in a club-organised setting. The purpose of this study is two-fold. First, it is to investigate whether family-related factors associated with a higher risk of social exclusion can be considered as determinants of club sport participation among children and adolescents. A second objective is to investigate whether the school, which is the second main socialisation agent in the life of children and adolescents, influences the likelihood of club-organised participation. Data are based on a large-scale cross-sectional survey (2009), collected in 39 schools, with a total of 3005 children and adolescents participating in the research. A multilevel logistic regression has been conducted. Results indicate club sport participation varies across schools, though only to a limited extent. Income poverty and parental education come forward as important determinants for club-organised sports participation. No evidence was found that living in a single parent-household affects the likelihood of club-organised sports participation. While sport is often considered as an important instrument for social inclusion, the study shows that children and adolescents who are likely to occupy a more vulnerable position in society as a whole, have higher odds to be left out with regard to sport club participation as well.