This study examined whether discourse and topic knowledge separately predicted the overall quality and the inclusion of basic genre elements in 5th grade students' stories, persuasive papers, and informational text once the other type of knowledge as well as topic interest, spelling, handwriting fluency, length of text, and gender were controlled. Fifty students (25 girls, 25 boys) wrote a story, persuasive paper, and informative text about outer space. In addition, students' discourse knowledge, knowledge about the writing topic, interest in the topic, and handwriting fluency were measured. Discourse knowledge made a unique and statistically significant contribution to the prediction of the quality and inclusion of genre-specific elements in story, persuasive, and informational writing beyond topic knowledge and 5 control variables (i.e., gender, topic interest, handwriting fluency, spelling accuracy, and text length). Topic knowledge also predicted story, persuasive, and informational writing quality beyond discourse knowledge and the 5 control variables. Further, topic knowledge predicted the inclusion of genre-specific elements in informational text. These findings supported the proposition that discourse and topic knowledge are important ingredients in children's writing and provided support for the architecture of the knowledge-telling model (Bereiter & Scardamalia, 1987).