The goal of this study was to investigate the development of mental lexicon organization among typical and dyslexic native Arabic readers. The participants included 271 students, divided into dyslexic readers, age-matched typical readers, and typical readers 2 years younger. The lexical status of root and pattern morphemes was examined using two priming paradigms: masked priming and the cross-modal immediate repetition task. We conducted two visual lexical decision tasks (Experiment 1 for verb pattern, Experiment 3 for verb roots), and two auditory decision tasks (Experiment 2 for verb pattern, Experiment 4 for verb roots). In the visual tasks, the participants were asked to decide whether a visual stimulus was a real word or not by pressing the laptop keyboard’s “yes” or “no” button. The auditory experiments were conducted similarly to the visual experiments, except that the stimuli were auditory, to clarify the locus of the morphological deficit observed in the visual test of the dyslexic students, should there be such failures. Analysis of Experiment 1 showed that verb patterns are not lexical entities with a role in organizing the mental lexicon among typical and dyslexic readers of different ages. However, Experiment 3 indicated that roots do indeed constitute lexical entities with a role in organizing the mental lexicon among normal and dyslexic readers of different ages. In Experiment 2, the auditory-morpho priming effect in the word pattern test was stronger among dyslexic and young readers than among more skilled readers, and contributed to speeding up lexical decisions more than its quality, among all research groups. In Experiment 4, the auditory-morpho priming effect in the root test was stronger than the visual effect among all participants, and contributed to hastening lexical decisions and improving the quality of the answers (success percentage). The results showed that roots contribute to the reading process. However, their contribution is different among dyslexic readers. Its construction is slower and different from that of typical readers, whereas word patterns have no lexical representation among the three reader groups that are likely to facilitate lexical decisions. The results are discussed with reference to the latest research literature on morpheme type (root or pattern).