Traditionally low retention in developmental courses (Bailey, Jeong, & Cho, 2010) has led to reformed models of developmental education such as corequisite developmental writing, in which students enroll in a college-level writing class at the same time as a developmental support course (Adams, Gearhart, Miller, & Roberts, 2009). The corequisite model represents a paradigm shift for the field as developmental writing instructors are no longer preparing students for college-level writing but supporting them within college classes. This qualitative case study focused on an experienced developmental instructor's beliefs and actions during the transition to corequisite developmental writing instruction at a Midwestern technical college. Analysis of interviews, observations, and course documents revealed that an instructor relied on her beliefs about writing instruction to guide her actions as she experienced both opportunities and tensions during the transition to the corequisite developmental writing model. Key opportunities in the transition included: (a) reflecting on the purpose of developmental writing instruction, (b) using extra time and small class sizes for individualized instruction, (c) employing contextualized, social approaches to instruction, and (d) understanding student error and motivations. Key tensions included: (a) competing views of the value of academic Discourse and grammar in writing instruction, (b) appropriately challenging and supporting all students within a single set of standards, (c) striking a balance between structure and flexibility, and (d) motivating students to value learning. Overall, the study illustrates the powerful relationship between beliefs and actions related to writing instruction. In transition to the corequisite model, an instructor relies on her beliefs to inform her actions so she can overcome challenges and take advantage of opportunities to support students. [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.]