This study examined whether discourse knowledge about various forms of writing predicted young developing writers' (Grade 2 and Grade 4 students) story writing performance once 4 writing (handwriting fluency, spelling, attitude toward writing, advanced planning) and 3 nonwriting (grade, gender, basic reading skills) variables were controlled. It also examined whether Grade 4 students (18 boys, 14 girls) possessed more discourse knowledge than Grade 2 students (18 boys, 14 girls). Students wrote a story and responded to a series of questions designed to elicit their declarative and procedural knowledge about the characteristics of good writing in general and stories in particular as well as their knowledge about how to write. Five aspects of this discourse knowledge (substantive, production, motivation, story elements, and irrelevant) together made a unique and significant contribution to the prediction of story quality, length, and vocabulary diversity beyond the 7 control variables. In addition, older students possessed greater knowledge about the role of substantive processes, motivation, and abilities in writing. Findings support the theoretical propositions that discourse knowledge is an important element in early writing development and that such knowledge is an integral part of the knowledge-telling approach to writing. (Contains 7 tables.)