Much of the literature on explicit teaching about language has suggested that equipping students with metalinguistic knowledge is as an important means of enhancing students' participation in learning. Yet in the context of international jurisdictions which are placing a renewed emphasis on knowledge about language, there is a notable lack of research into the nature of learners' metalinguistic understanding about writing, as evident in their ability to reflect on written language. Using an analytical framework shaped by Vygotsky's and Hallidayan theories of concept formation and language learning, this paper provides insights into the nature of metalinguistic understanding as manifested in ways in which learners engage with grammatical concepts. Drawing on data selected from two parallel studies in Australia and England in which students aged 9-13 were interviewed about their metalinguistic understanding of writing, our analysis has found that learners' metalinguistic understanding is more strongly oriented to identification - naming and specifying taught grammatical concepts. The findings have important implications for pedagogical strategies that might facilitate higher-level metalinguistic understanding, enabling learners to elaborate, extend and apply their grammatical knowledge.