An auditory lexical decision experiment was conducted to find out whether sound-to-spelling consistency has an impact on German spoken word processing, and whether such an impact is different at different stages of reading development. Four groups of readers (school children in the second, third and fifth grades, and university students) participated in a lexical decision experiment. They were presented with spoken monosyllabic words that had either orthographically consistent rimes (i.e., there is only one spelling for the phonological rime) or orthographically inconsistent rimes (i.e., there are words with the same phonological rime but a different rime spelling). Results reveal that sound-to-spelling consistency influences spoken word processing in early and advanced stages of reading development in German. This finding indicates that word spelling knowledge gets intertwined with knowledge about phonological word forms early during reading acquisition.