Diglossia and Orthographic Complexity as Multiplicative but not Additive Challenges in Arabic: A Critical Review.

The present review explores how the unique linguistic and orthographic characteristics of Arabic interact to shape the development of literacy in Arabic. The review is based on a systematic synthesis of empirical studies published between 2000 and 2025, including behavioral, developmental, and neurocognitive research on reading, spelling, and comprehension among native Arabic speaking learners, conducted in line with PRISMA guidelines. It focuses on the combined influence of diglossia and the visual and structural complexity of the Arabic script. Drawing on empirical findings from behavioral, developmental, and neurocognitive research, the review shows that these two dimensions do not merely add their effects but interact in a multiplicative way, creating cumulative challenges for beginning readers and for those with reading difficulties. Across the studies reviewed, a consistent pattern emerges showing that this interaction constrains decoding accuracy, reading fluency, and comprehension across developmental stages. These effects are particularly evident in the early phases of literacy acquisition and are amplified among learners with dyslexia or developmental language disorder. The discussion critically examines how universal models of reading fail to account for these interacting sources of difficulty, and argues for a language-specific framework that captures the dynamic relation between phonological, morphological, and orthographic processes in Arabic. From an instructional perspective, the synthesis points to the need for teaching practices that explicitly bridge spoken and standard varieties of Arabic, place greater emphasis on morphological awareness, and provide careful scaffolding as learners transition from vowelized to unvowelized text. The review concludes with implications for theory and pedagogy, emphasizing the need for instructional practices that bridge spoken and standard Arabic.