This study examines the construct and principles of reading achievement assessment from a sociocultural perspective and offers implications for developing a large-scale reading assessment framework in Korea. To begin, prior research in educational measurement and the learning sciences is reviewed to clarify the concept of validity grounded in sociocultural constructivism. Subsequently, the 2026 NAEP Reading Framework is analyzed to identify how the framework incorporates contemporary theories of reading and addresses current societal demands in its development and design. The analysis highlights five key features: (1) a socioculturally informed construct model of reading; (2) specification of reading purposes and text selection aligned with disciplinary contexts; (3) scenario-based task design; (4) integration of universal design principles to account for learner diversity; and (5) a reporting system that incorporates sociocultural contextual variables. Building on these findings, this study proposes considerations for designing socioculturally oriented reading assessments in the Korean context. By reconceptualizing reading assessment as a sociocultural practice, the study contributes theoretical and practical foundations for future literacy education and assessment policy development.