The rapid decline in Australian students' performance on the "National Assessment Program--Literacy and Numeracy" (NAPLAN) writing test is an issue of national concern. This paper presents the first investigation into patterns of achievement and progress on the NAPLAN writing test across the tested year levels (3, 5, 7 and 9) between 2011 and 2018, with a focus on gender differences. The findings reveal a considerable decline in writing performance for both genders over time, with a major disparity of up to 2 years of learning in test outcomes between male and female students. While performance of girls exceeded year-level standards when averaged over the 8 years, the average performance of boys was consistently below standards, with male students falling further behind female students across the school years. Yet average scores for both genders have declined significantly since 2011. Drawing on current international research into the teaching of writing and standardised writing tests, the paper considers two possible causes for this decline which are often communicated by education stakeholders: ineffective writing instruction, and issues with the design and implementation of the NAPLAN writing test. The paper calls for a national conversation about how we might effectively teach and assess writing.