Previous studies reveal that young Dutch children display a [t]-bias in the middle of words in pronunciation (e.g. van der Feest 2007; Kerkhoff 2007). First graders, however, display a 〈d〉-bias in the middle of words in their writings (Neijt & Schreuder 2007). The present study investigates children’s spelling and pronunciation of word medial d and t to examine this apparent contrast. It turned out that first graders started with a 〈t〉-bias in their spellings while later on they displayed a 〈d〉-bias. A similar development was found for pronunciation: Kindergartners displayed a [t]-bias, while second graders displayed a [d]-bias instead. Our explanation is that this change is caused by overgeneralization, due to differences between Dutch pronunciation and orthography. We conclude that the orthographic system, although learned later in life, affects children’s earlier acquired pronunciation.