The International Dyslexia Association defines dyslexia as unexpected problems of neurobiological origin in accuracy and rate of oral reading of single real words, single pseudowords, or text or of written spelling. However, prior research has focused more on the reading than the spelling problems of students with dyslexia. A test battery was administered to 122 children who met inclusion criteria for dyslexia and qualified their families for participation in a family genetics study that has been ongoing for over a decade. Their parents completed the same test battery. Although a past structural equation modeling study of typically developing children identified a significant path from handwriting to composition quality, the current structural equation modeling study identified a significant path from spelling to composition for children and their parents with dyslexia. Graphomotor planning did not contribute uniquely to their composition, showing that writing is not just a motor skill. Students with dyslexia do have a problem in automatic letter writing and naming, which was related to impaired inhibition and verbal fluency, and may explain their spelling problems. Results are discussed in reference to the importance of providing explicit instruction in the phonological, orthographic, and morphological processes of spelling and in composition to students with dyslexia and not only offering accommodation for their writing problems. Keywords dyslexia; writing disability; motor skills; automatic handwriting; spelling; written composition 2 Grant P50 33812-06 to -08 from the National Institute of Child Health and Human Development (NICHD) supported this research.Results were presented at the International Neuropsychological Society Meeting in Dublin, Ireland, July 9, 2005. 3 The authors thank Joan Waiss for assistance in scheduling families, and Allison Brooks, Rebecca Brooksher Pirie, Kate Eschen, Sarah Hellwege, Diana Hoffer, Stephanie King, and Dori Zook for administration of the phenotyping test battery to participants and Jon Organ for assistance in preparing the tables. Most of all they acknowledge the contribution to this research of the families who are affected across generations by dyslexia, including the children and their parents.Correspondence to first author at 322 Miller, Box 353600, University of Washington, Seattle, or vwb@u.washington.edu,. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. The current definition of dyslexia recommended by the International Dyslexia Association is unexpectedly low accuracy and/or rate of oral reading or spelling of ne...