Complex noun phrases (NP) are central to mature academic writing and often a focus of explicit teaching. The National Curriculum in England, for example, requires specific components of NP complexity to be taught at specific educational stages. However, the evidence base for such practices is unclear. Research on the emergence of NP components is both limited and dated. Moreover, some work has suggested that NP development is late-occurring and genre-specific, calling into question curricular guidance which specifies teaching from the earliest years and which makes no mention of genre. Analysing 240 texts written by children in England aged six to 16, this study shows that overall complexity develops at a roughly constant rate from primary school onwards. Increases are principally driven by postmodification, especially relative clauses and proposition phrases. By the end of their mandatory education, children make some use of genre distinctions evident in adult writing. However, there are also clear patterns of overuse and underuse of particular NP components. Key distinctive features are examined in context to understand the roles NP components play in writing development.