This study investigated fourth and fifth graders' metacognitive knowledge about writing and its relationship to writing performance to help identify areas that might be leveraged when designing effective writing instruction. Students' metacognitive knowledge was probed using a 30-minute informative writing prompt requiring students to teach their reader how to be a good writer (i.e., a metawriting task). The metawriting task was coded for eight dimensions of metacognitive knowledge. Students' writing performance was assessed via additional 30-minute prompts--two narrative, one informative, two persuasive--and evaluated for quality and length using automated essay scoring. Students were most aware of general characteristics of writing quality and production procedures, but they were less aware of substantive processes, genre, or other dimensions. Multiple regression analysis showed that, after controlling for demographics and literacy skills, only knowledge of general characteristics of writing and production procedures uniquely predicted outcomes. Overall, metacognitive writing knowledge inconsistently predicted writing performance.