Kelly Gallagher writes that "wide swaths of students are not developing their writing skills--skills we know to be foundational to their literate lives." In this article, he explains how school districts can go about developing students' writing skills in all content-area classrooms. He highlights five reasons why students should write in the disciplines, including to generate deeper thinking, to become career ready, to become college ready, to prepare for state tests, and--most important--to develop into lifelong writers. Gallagher profiles Anaheim Union High School District in California as an example of a district that is going about this work, describing in detail how educators have prepared to become teachers of writing in every classroom.