Objective: This study examined the relationship between ADHD and writing performance. Method: Students in Grades 3 to 7, 84 with ADHD and 135 age and gender-matched controls completed a writing task (including process logs), and measures of, working memory and attention. Results: Students with ADHD wrote texts of similar length but with poorer structure, coherence and ideation. 6.7% of the variance in writing quality was explained by whether or not the student had an ADHD diagnosis, after control for IQ and age-within-year, with students with ADHD producing text that was less coherent, well structured, and ideationally rich and to spend less time thinking about and reviewing their text. Half of the effect on text quality could be attributed to working memory and sustained attention effects. Conclusions: ADHD has some effect on writing performance which can, in part, be explained by working memory and attentional deficits.