Knowing how to write is critical to students' post-secondary success, yet concerns with students' writing have persisted for nearly four decades. Few reports, however, document high school English teachers' lack of preparation to teach writing or the pressures they face as they negotiate accountability policies and diverse student need. This negotiation directly impacts teachers' instructional decisions and, ultimately, the conditions in which students learn to write. Using a two-phase, mixed methods approach, this dissertation study examines three factors related to high school English teachers' instruction of writing: teachers' perceived knowledge of writing instruction, their students' diverse needs related to writing, and the pressures of high stakes accountability policies. Specifically, within this study I examine the tensions that arise as teachers negotiate these three factors and the ways in which the tensions teachers experience vary depending on teachers' knowledge of writing instruction, the diverse needs of their students, and local accountability pressures. The first phase of the study included a 40-item survey administered to 171 high school English teachers who taught a representative sample of California high school students. Survey results were analyzed first using descriptive statistics and then using Principal Components Analysis. Preliminary findings from the survey informed participant selection for phase two, case studies of eight teachers. Data collected from each case study teacher included beginning and end-of-year interviews, one to two-day observations at four points in the school year, and collection of instructional documents related to writing. Together, the two phases yield nuanced understandings of the interplay of teacher knowledge, student need, and accountability policies on writing instruction. Findings from the survey illustrated that teachers in all but the highest performing schools (according to Academic Performance Index score) faced pressures from various accountability policies that impacted their instruction of writing. These findings were further substantiated by data collected from the case study teachers. Additionally, although survey respondents overall reported that they had the necessary knowledge to teach writing to their students, case study findings illustrated that most teachers receive little formal preparation to teach writing. Ultimately, accountability policies had the biggest impact on what writing was taught. Taken together, the results of this study demonstrate the need for more attention to writing in both teachers' pre-service teacher preparation and in-service professional development. Additionally, the results illustrate the impact of the current high stakes accountability assessment on high school teachers' instruction of writing. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]