This ethnographic case study investigated literacy instruction and intervention practices within a Multi-Tiered Systems of Support (MTSS) framework in upper elementary school. Multi-Tiered Systems of Support has been proposed as a system of schoolwide reform aimed to support students' academic and social-emotional development and is often used with Response- to-Intervention, a model designed to prevent learning difficulties and to provide differentiated assistance to identified students. Both MTSS and RTI have been proposed to advance equity for the learning experiences of historically marginalized students in school. I used ethnographic case study methodology to offer an in-depth exploration into literacy instructional and intervention practices at one elementary school working to implement an MTSS framework. My analysis was guided by cultural-historical activity theory (CHAT), which provided a lens into the role of personal, interpersonal, and cultural-institutional factors that impact instructional decision-making and children's literacy experiences. I explored how the activity systems of core instruction, tiered interventions, data and assessment culture, and MTSS instructional decision-making interacted to inform instruction and to mediate upper elementary students' reading-related identities, practices, and experiences. Focal participants were five students in fourth and fifth grade as well as 10 other participants, including classroom ELA teachers, school leadership personnel, teachers who provide additional reading support, and parents. I spent one year with participants in the school and conducted over 145 hours of classroom observations and 21 semi-structured interviews. I used constant comparative analysis and activity systems analysis to generate findings. My analysis demonstrated that conflicting priorities and responsibilities impacted MTSS program implementation and mediated upper elementary students' literacy learning, practices, and identities. First, upper elementary teachers and school leaders wrestled with conflicting tensions to develop students as readers versus teaching reading as a set of test-taking strategies. Second, school personnel conceptualized and operationalized data literacy in contradictory ways, as data literacy to promote ELA standards proficiency was often in tension with efforts to use data literacy for MTSS decision-making. Finally, as teachers navigated multiple demands and responsibilities, they also encountered cultural-institutional fragilities within the school, including scheduling, staffing, district and state initiatives, and behavior support. These tensions and conflicting demands contributed to inconsistent MTSS program implementation and created challenges to providing literacy support to focal students. Findings from this study indicate the need for improved and reimagined systems of reading support for students, teachers, and school leaders in upper elementary school, and directions for future research are offered. [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.]