Background: Letter knowledge is crucial in the first stages of reading development. It supports learning letter-sound mappings and the identification of the letters that make up words. Previous studies have investigated the longitudinal impact of early letter knowledge on children's further word reading abilities. This study employed an artificial orthography learning paradigm to explore whether the rate of letter learning modulates children's reading and word identification skills. Methods: In an initial training phase, 8-year-old Spanish children (N = 30) learned nine artificial letters and their corresponding sounds (two vowels and six consonants). The letter learning rate was set according to the number of attempts needed to name at least seven letters (i.e., 80% correct). These ranged from 1 to 4. In a second training phase, children visualized words made up of the trained letters while listening to their pronunciations. Some words included a context-dependent syllable (i.e., leading to grapheme-to-phoneme inconsistency), and others had an inconsistent syllable (i.e., phoneme-to-grapheme inconsistency). The post-test consisted of a reading aloud task and an orthographic-choice task in which the target word was presented with a distractor equal to the target except for the substitution of a letter. Results: Children showed a high accuracy rate in the post-test tasks, regardless of whether words contained context-dependent or inconsistent syllables. Critically, the letter learning rate predicted both reading aloud and identification accuracy of words in the artificial orthography. Conclusions: We provide evidence for the vital role of letter knowledge acquisition ability in children's decoding and word identification skills. Training children on this ability facilitates serial letter-sound mapping and word identification skills. Artificial orthography paradigms are optimal for exploring children's potential to achieve specific literacy skills.