Effective writing is to some degree characterised by the ability to use complex grammatical structures. However, grammatical complexity is poorly defined in linguistics and related disciplines such as literacy. This empirical study examined the notion of grammatical complexity and its relevance to literacy. Complexity is multifaceted, so for reasons of scope the study was confined to nominal structures, i.e. the noun phrase (e.g. "I finished the book on Marx") and the nominal clause (e.g. "I heard what you were doing"). Such nominal structures were analysed by frequency and category in a bank of essays from Year 10/11 pupils in a UK comprehensive school. The results suggest that complexity is a product of the interaction of grammar with the context of production, and that in literacy it is helpful to view grammar as a system of options that can be manipulated to maximise the meaning potential of a text.