Students with Attention Deficit Hyperactivity Disorders (ADHD) frequently experience significant difficulty mastering basic academic skills. This meta-analysis focuses on one specific potential area of learning difficulties for these students: namely, writing. To identify the extent and depth of the potential writing challenges faced by students with ADHD, we conducted a meta-analysis comparing the writing performance of grade 1 to 12 students with ADHD to their normally achieving peers. We located 44 papers, yielding 45 studies with 87 effect sizes. The average weighted effect sizes showed that students with ADHD obtained lower scores than their normally achieving peers for writing quality (-0.78), output (-0.64), number of genre elements (-0.69), vocabulary (-0.76), spelling (-0.80), and handwriting (-0.62). Contrary to expectations, moderator analyses found that neither study quality nor the source from which ADHD students were drawn (i.e., school/community vs. clinic/hospital) accounted for variability above sampling error alone.