Abstract
This study investigated whether adults with long-standing reading difficulties ("poor readers") can acquire new literacy skills in both familiar (English pseudowords) and novel (artificial orthography, AO) systems, and how phonological decoding deficits relate to orthographic learning. Poor readers (n = 17) and matched typical readers (n = 17) completed a decoding task and three orthographic learning tasks (spelling, identification, and lexical decision) in both orthographies. Results showed that poor readers achieved near-ceiling accuracy in learning novel grapheme-phoneme correspondences, yet remained less fluent than typical readers across both orthographies, even after repeated practice. Despite this persistent fluency gap, poor readers performed comparably to typical readers on measures of orthographic learning, indicating that decoding efficiency does not directly constrain orthographic acquisition under conditions of equal exposure. Exploratory cluster analyses revealed heterogeneous profiles among poor readers, with distinct constellations of cognitive strengths and weaknesses shaping decoding outcomes. These findings highlight fluency as the central bottleneck in adult literacy while demonstrating that adult readers with long-standing reading difficulties can form accurate orthographic representations through structured practice. The results also highlight the importance of considering individual variability in both research and adult literacy interventions.