The present research traces the second language learning process in Luxembourgish during book related activities by 4- to 5-year old pre-schoolers with Portuguese, Cap Verdean and Brazilian origins. With 47,2% of the preschool population being of foreign origins, the Lusophone community forms the largest group with 24,1%. This salient fast growing multilingual and multicultural population learns Luxembourgish for integration and everyday interaction and, hence, challenges public education with its diverse and altering demands. The present study enlarges second language research in the Luxembourgish context and links to previous investigation on topics, however, by taking a pragmatic stance towards topics. Through the foregrounding of the local topic management as well as its impact on activities, which are less teacher controlled, the study pictures second language learning as a product of co-constructed interaction. The focus lies on the negotiation of story meaning through self-initiated topic changes during three book related activities: Joint reading, storytelling and play. The data consists of video recorded lessons and on stimulated recall interviews with the teachers. A multi-method framework is used to investigate pupils’ interaction and language learning processes. From a quantitative point of view, the study analyses how pupils’ utterance length varies according to the openness of the lesson by allowing self-initiated topic changes as well as the design of the book activity (1) led by teachers or (2) by the pupils. From a qualitative stance, a sequence-by-sequence analysis of the jointly constructed narrative identifies the interactional dynamics of the collaborative storytelling activities and the use of self-initiated topic changes which children draw upon to express themselves more freely. The results show that children’s utterances vary according to the activity type. Pupils produce longer utterances, when they can self-initiate a topic hereby boosting their second language proficiency – either ...