Phonological awareness and letter knowledge have been shown to be precursors of children’s word reading and reading comprehension. As a consequence, promoting children’s phonological awareness should result in better reading skills. In order to evaluate this assumption, we trained phonological awareness and letter knowledge of 370 German preschool children and compared their word reading and reading comprehension skills with those of a group of 99 untrained children. Our findings indicate strong intervention effects on children’s phonological awareness and letter knowledge. However, this advantage did not result in better reading skills in general. Within the group of low-performing children, we found small effects on word reading. This effect was mediated by individual differences in phonological awareness. In summary, only for low-performing children do the findings support our theoretical assumptions. This may be attributable to differences in the orthographic transparency between German and English, which restricts a generalization of findings across languages.