In this thesis, I explore the associations between participation in organized activities, class, and academic achievement among upper secondary school students in Oslo. Sociological research concludes that social origin is linked to activity participation and this is a source of unequal academic achievement. However, little is known about how participation in organized activities is associated with academic achievement in Norway. Three research questions are posed: (1) What is the relation between parental economic and cultural resources and activity participation? (2) What is the association between activity participation and academic achievement? (3) How is the association between activity participation and academic achievement affected by socioeconomic background? I use the survey “Young in Oslo 2018” with a subsample of upper secondary students and investigate the research questions using logistic and ordinary least regression techniques. Throughout the thesis, I argue that we need to consider social inequality when researching youth participation in organized activities. Recent theoretical contributions disagree on whether unequal participation is primarily influenced by financial or cultural resources. I investigate how these different types of parental resources affect the chances of participation in organized activities. I find that the impact of cultural and financial resources differs according to the type of activity, while the impact does not vary when exploring activity participation in general. I argue that we need to understand both the role of economic and cultural factors when facilitating participation in organized activities. Moreover, I examine the association between activity participation and academic achievement. I find a positive association between activity participation in structured activities such as sports teams and cultural activities and academic achievement. In contrast, I find a negative association between participation in youth clubs and academic achievement. I argue that the role of structure in the activity context is vital for understanding why some activities are associated with positive outcomes. Finally, I examine interactions between activity participation and social background. I find that students with high socioeconomic backgrounds show a positive significant association between activity participation and academic achievement, while students with low socioeconomic backgrounds do not. I discuss how families prepare youth unequally for activity participation and how this can explain why some groups seem to benefit more from organized activities than other. Additionally, I discuss methodological issues such as conceptions of activity participation, causality, and selection bias, and point to the need for further research on the topic.