The aim of this study was to examine the effect of oral and written language input on the development of phonological awareness (PA) in 4-, 5-, and 6-year-old children. The abilities of Czech and English speakers were contrasted because these two languages differ considerably both with respect to syllable structure (oral language) and in orthographic depth (written language). Czech contains a greater variety and frequency of complex syllabic onsets than English. Also, the Czech orthography is transparent whereas English orthography is opaque. It was hypothesized that if language input affects children′ s PA development, Czech children should show higher levels of awareness for complex onsets prior to formal schooling. The Czech first graders should show greater improvement in PA skills than their Anglophone peers as well as better spelling skills after formal exposure to reading.