This article presents a study of written development in English as a foreign language produced in a content and language integrated learning (CLIL) environment. The texts analysed, from history classes, were collected annually over the four-year obligatory junior secondary education program from the same students (aged 12 to 16), in two state schools in Madrid, Spain. The ability to produce coherent texts and the appropriate management of the nominal group, or noun phrase, to create disciplinary registers are key skills for academic writing. With the purpose of identifying the linguistic resources used to create coherence and appropriate register in the CLIL students' written texts, all the nominal groups in the corpus were analysed in terms of recoverability of the elements they referred to, further classifying the referential elements into different types. Finally, the structure of the nominal groups was analysed for pre- and post-modification. The results show development in the control of textual resources, as well as some increase in nominal group complexity, over the four years. The study suggests that CLIL settings, which focus primarily on the learning of content, provide suitable contexts in which to develop written discourse, since the students can draw on a solid knowledge base from which to create their text. Students need to be given the opportunity to construct scaffolded but longer and more autonomous texts in the required genres, an ability which is inextricably linked to academic success in the content area. (Contains 3 figures and 4 tables.)