The Common European Framework of Reference (CEFR) was used to develop guidelines for the provision of English L2 support for newcomer children in Irish primary schools. The guidelines present age-appropriate and domain-specific 'can do' descriptors for the first three levels of the CEFR (A1–B1). This book reports on an in-depth empirical investigation of the English L2 development of 18 primary pupils over the course of one school year. It presents case studies which illustrate the often uncertain progress of pupils' language development, and examines the wide range of variance across the sample. It also provides an analysis of the data as a whole, which reveals a number of regular patterns. The findings confirm that pupils' communicative capacity developed according to the functional trajectory proposed by the guidelines and derived from the CEFR; they also allow us to attach a great deal of linguistic detail to descriptors of underlying linguistic competence.