First-year composition (FYC) has historically functioned as a space for furthering the linguistic assimilation of students into "appropriate" forms of communication in academic spaces. While often going unstated in course/writing program goals, Standardized American English (SAE) has typically been the language variety elevated in FYC classrooms. As SAE is associated with White individuals, the (un)spoken privileging of this variety in the classroom has been heavily critiqued as a way of furthering White supremacy. Further research into specifically how uncritical writing pedagogies can work to foster environments of White supremacy is one necessary avenue for further inquiry. In particular, research into how the language ideologies, or beliefs about language, may contribute to or resist these systemic problems can help understand the motivations instructors may have in enacting various pedagogical practices. To engage in such research, I completed a two-semester participatory action research project (PAR) with White instructors to examine their language ideologies and how those ideologies may influence their FYC pedagogies. Through focus groups, interviews, surveys, and on-going discussion groups with White lecturers and graduate student instructors, I collected and coded numerous transcripts and classroom documents (e.g., syllabi, assessments, feedback on student papers, et cetera). In building off of findings from relevant research in writing studies, linguistics, and whiteness studies, I identified and coded for a variety of themes relevant to assessment strategies, explicit and implicit race discussions, as well as attempts at antiracist pedagogical practices to uncover the language ideologies that motivated instructors and how those ideologies responded to various writing and student constructs. The findings of this work are wide-ranging and identify multiple, intersecting challenges for creating more linguistically just FYC classroom spaces and practices. In summary, however, the findings of this project identified how White instructors avoid explicit acknowledgments of race in pedagogical discussions and classroom materials. This color-blind approach extended to how they viewed whiteness as well, as often felt trapped by discourse of whiteness and privilege. Additionally, the White instructors shifted toward expressing more anti-racist/non-SLI pedagogies in group sessions than when in individual settings, further creating questions around sincerity and participation Within their classroom practices, further findings from this research indicate that White instructors may identify instances of students of color using non-SAE varieties as being more authentic and instances of SAE as being performative. These many tensions seem to surface most explicitly in discussing assessment, as White instructors seem to experience a great degree of uncertainty when assessing writing. Responding to these tensions, they may utilize cooperative forms of assessment (e.g. negotiations and self-assessments) in an attempt to both be more linguistically inclusive but also to shift responsibility for assessment away from just themselves. Following discussion of these findings, I label the language ideologies observed in this data as White Supremacist Language Ideologies (WSLI), a term I define and unpack further with specific examples and patterns of enactment found in this research. Lastly, this dissertation points to more critical language pedagogies as being one possible response to these intersecting issues by providing both examples of what these pedagogies might look like and further areas of investigation for writing programs to consider how WSLI may function in their writing spaces. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]