Being literate in the twenty-first century demands individuals to create and interpret patterns of meaning that may be visual, audio, gestural, tactile and spatial (Kalantzis & Cope, 2012). While writing is one central part of being literate as it provides a means for personal reflection, creativity and intellectual inquiry, how important is it to learn basic written language skills at school, such as spelling, grammar and punctuation? This paper draws on data from 819 Australian primary school students to explore the relationship between three language convention variables (spelling, grammar and punctuation) and written composition, as measured by the National Assessment Program Literacy and Numeracy (NAPLAN) Language Conventions Test and the Writing Test. Findings for the study indicate that spelling, grammar and punctuation jointly influence written composition, and that spelling is the main predictor of written composition. Implications for the educational practice of writing in the contemporary context are discussed.