This thesis aims to understand the multi-layered experiences of children labelled as having English as an additional language (EAL) in changing contexts by focusing on academic and social experiences in their transition from primary to secondary school. Although from a school perspective EAL is often linked with knowledge and proficiency in the English language as a means to access learning, this study builds on the complexity underlying the term that incorporates background, culture, agency and power in the ways children navigate their schooling. This is achieved through in-depth longitudinal accounts of children's experiences and engagement co-constructed with participants and triangulated through interactive qualitative methods and theoretical lenses. The main focus is the active role of children in finding and embracing opportunities for social and academic engagement as part of their educational trajectories, identifying their agency in processes of change in the contrast between formal academic contexts and informal research discussions. In order to learn more about young people's academic and social experiences, the study is theoretically informed by two perspectives. The first perspective is Bourdieu's field analysis and the concepts of habitus, dispositions and agency. The analysis emphasises how and where children use their agency to engage with and manage expectations and options highlighted by institutional discourses and teachers. Looking at children's experience and engagement explicitly, the research highlights overlooked agency of children too easily categorised as EAL in the school field. The second analytical perspective explores engagement and trajectories in a classroom context and draws on Bernstein's constructs of classification and framing with the aim to explain how children engage and reflect on their experiences across differently structured classroom contexts. Drawing on theoretical constructs and research in the area of EAL and diversity more widely, I present six case studies of children's experiences. I demonstrate that in the case of children categorised as having EAL the social and academic aspects of learning highlight invisible agency, misinterpreted engagement and active negotiation of positioning. Learning English to access learning was not a central feature of the cases. I argue that in the light of gaps in teachers' understandings of children's experiences, theoretical interpretations, practical adjustments to classroom processes and communication could provide better understanding of the wider scope of children's experiences of schooling. In this study, children labelled as having EAL are the group whose transition stories are voiced, and EAL had only a limited role.