Out-of-school time programs can offer a secure and nurturing environment for children and adolescents, reducing the worries about what they are doing during these most vulnerable hours. For example, research suggests that participation in out-of-school time programs and activities can lessen the likelihood that children and adolescents will engage in negative behaviors, such as using drugs and alcohol, dropping out of school, and practicing unhealthy eating habits. Despite the benefits associated with this involvement, millions of children between the ages of 5 and 14 still do not participate in these programs. Most research on participation in out-of-school time programs has examined markers that predict participation (or non-participation) in certain contexts and outcomes associated with this participation. Very little research has been done on individual factors (such as health status, academic achievement, and behavior problems) and background factors (such as family characteristics) that influence children and adolescents' non-participation in out-of-school time programs and activities. This brief examines these other factors. Findings indicate that, overall, child, family, and neighborhood factors matter. Results from our analyses indicate that child, family, and neighborhood factors were all associated with non-participation in out-of-school time programs and activities. (Contains 1 table and 2 footnotes.)