For the teaching of writing across disciplines, teachers need to use formative assessments to document student learning and to direct their instructional decision making. Using genre-specific rubrics is a strategy that can be used across disciplines. The content of the rubrics should differ to reflect the norms, practices and discourses of those disciplines. The primary purpose of this chapter is to provide (a) a description of an analytic persuasive writing rubric to assess students' disciplinary writing and (b) guidance as to how practitioners can use this rubric to make data-driven decisions about students' writing instruction within various disciplines. This chapter provides an authentic teaching scenario involving students with learning disabilities and attention deficit disorder.