Literacy standards increasingly emphasize the importance of analytic text-based writing. Little consensus exists, however, around what high-quality student responses should look like in this genre. In this study, we investigated fifth-grade students' writing in response to analytic text-based writing tasks (15 teachers, 44 writing tasks, 88 pieces of student writing). We used qualitative analytic techniques to investigate teachers' stated assessment criteria and to compare teachers' and researchers' assessments of student writing nominated by teachers as high quality. We then characterized patterns in students' responses. Our results showed no variation in teachers' stated assessment criteria but substantial variation in students' writing with respect to 3 researcher-defined elements: cognitive process, use of text evidence, and explication. Only 22% of student responses nominated by teachers as high quality were close to fully realizing the task potential.