This paper examines one child’s L2 (speaking and writing) development in social contexts of learning over a six-month period from the age of seven years and five months. It describes L2 development during the first months of the child’s schooling and interprets it in terms of a socio-semantic approach to language learning. The study, which adopts a qualitative approach in an interpretivist/constructionist research paradigm, entailed the collection and interpretation of data through multiple sources: observation, interviews, and written and spoken texts. The analytical framework is provided by systemic functional linguistics and an overall theoretical framework is formed by Vygotsky’s and Halliday’s theories. The results show that the child’s ability to encode meaning became increasingly rich over the research period; the child’s meaning making potential expanded and her thinking became conscious as her L2 developed. The child’s L2 learning took place in social contexts involving herself with others. The paper argues that these social relationships substantially drove the child’s L2 development, in addition to effectively enhancing her writing and speaking, suggesting that the language learner needs to learn to use language in social interaction.