<p>This study investigated the time course of learning letter and speech sound (LS) associations in Polish-speaking children, an ability essential for reading acquisition. The research engaged 337 children from kindergarten through 8th grade, evaluating their ability to match LS via a computer-based LS congruency judgment (LSCJ) task. Results highlighted significant variations in LS matching accuracy and reaction times across different grades, with overall improvement observed as children progressed in their formal education. Notably, most children achieved 80% accuracy after one year of literacy instruction. At the same time, we observed a steady decrease in reaction times until the final grades of primary school, in line with previous observations in Dutch children. A strong correlation was established between LS matching accuracy and fluency and broader reading and phonological skills. Utilizing a Bayesian model averaging approach, predictive models for word reading were developed for younger (up to 2nd grade) and older children. The findings indicated that letter knowledge and rapid automatized naming (RAN) of objects are important predictors of word reading for younger children. For older children, reaction time in the LSCJ task and advanced phonological skills were identified as strong predictors of reading ability, emphasizing the dynamic nature of reading predictors as children develop. Overall, these findings underscore the critical role of early LS knowledge in literacy development, suggesting that targeted interventions to strengthen the fluency of these associations could be beneficial in educational settings. This research contributes valuable insights into the pace and predictors of reading skill acquisition in a transparent language, offering implications for effective literacy instruction and support strategies.</p>