Orthographic learning is one of the steps needed to achieve reading fluency. There are different variables that could influence the formation of orthographic representations. The aim of this study was to investigate the role of the previous semantic and phonological knowledge on the formation of orthographic representations. We used a decrease of the length effect as the measure of orthographic learning. We made a reading aloud task that utilised new words with Spanish children from third grade under three different conditions: with prior semantic and phonological training, with prior phonological training and without training. Results showed that knowing the meaning and the phonological form of the words facilitated the formation of orthographic representations, as the length effect was significantly lower than in the other conditions, and it also improved the children's reading performance.