A dyslexia program developed and validated in English, applied without adaptation to Finnish, Spanish, or Greek, will allocate instructional time sub-optimally. Here's why: In shallow (transparent) orthographies — Finnish, Italian, Spanish, Modern Greek — dyslexia presents primarily as a fluency deficit, with relatively preserved accuracy. In deep (opaque) orthographies — English is the canonical example — dyslexia presents as both an accuracy and a fluency deficit. The instr