We modeled word reading growth in typically developing (n = 118) and children with dyslexia (n = 20), Grades 2-5, across multiple exposures to 30 words. We explored the facilitative versus inhibitory effects of exposures to differential mixes of words that support high- versus low-frequency vowel pronunciations. One training corpus contained a ratio of 80%-20% high- to low-frequency pronunciations (e.g., for "ea"; 80% "ea" pronounced as /i/ as in "bead" and 20% "ea" pronounced /[epsilon]/ as in "dead"), whereas the other consisted of a ratio of 20%-80%. We also modeled accuracy at the final exposure for a subset of 12 shared words across conditions using item-level crossed-random effects models with reading skill (i.e., typically developing vs. dyslexic), condition, word frequency, and vowel pronunciation (i.e., high- vs. low-frequency vowel pronunciation) as predictors in the model. We were particularly interested in the interaction between condition and vowel pronunciation across reading groups. Results suggest typically developing children were influenced by the interaction between condition and vowel pronunciation, suggesting both facilitation and inhibition, whereas children with dyslexia were influenced by condition and vowel pronunciation without an interaction. Results are interpreted within the overfitting model of dyslexia.