Abstract
The disparity in reading ability among first-grade elementary school students results from the wide variation in children's literacy readiness upon entering primary education, as reflected in four categories of initial reading ability found within a single class: not yet recognizing letters, recognizing letters but unable to read, beginning to read words, and reading fluently. This study employs Carol Ann Tomlinson's Differentiated Instruction Theory as the primary framework for analyzing how first-grade teachers implement strategies to address this gap, while also drawing on Vygotsky's scaffolding theory and Bronfenbrenner's ecological systems theory to deepen the discussion. The study aims to: (1) describe the implementation of differentiated instruction applied by first-grade teachers; (2) identify the forms of content, process, and product differentiation used; and (3) explain the supporting and inhibiting factors of its implementation, including their relationship to children's literacy transition from early childhood education to elementary school. The study employs a descriptive qualitative approach with a case study design, using in-depth interviews with first-grade and kindergarten teachers, classroom observation, and documentation study, analyzed through the interactive model of Miles, Huberman, and Saldãna. The results show that teachers implement initial-ability mapping, flexible student grouping, and the provision of tiered instructional materials as forms of content differentiation, along with individual assistance and peer tutoring as forms of process differentiation, while product differentiation was not explicitly identified in the research data. Supporting factors for implementation include school policies that prioritize foundational literacy and the availability of instructional media, while the main inhibiting factors include curriculum demands emphasizing comprehension and critical thinking from the first grade onward, limited time for individual assistance, dependence on parental cooperation, and weak coordination between kindergartens and elementary schools regarding children's literacy-readiness standards. The study concludes that differentiated instruction is an effective mitigation strategy at the classroom level, but its sustainability requires stronger, more integrated early-childhood-to-elementary transition policies.