Nonword repetition tasks (NWRTs) are employed widely in various studies on language development and are often relied upon as diagnostic tools. However, the mechanisms that underlie children's performance in NWRTs are very little understood. In this paper we present NWRT data from typically developing 5- to 6-year-olds (5:4-6:8) and examine the pattern of their phonological errors within the syllabic domain. We show that the children display a strong tendency for errors at the syllable onset, with fewer errors in coda position. We then show how the same pattern can be simulated by a computer model, thus shedding some light on the cognitive mechanisms that underlie specific error patterns as well as general phonological development. (Contains 9 figures, 7 tables, and 22 footnotes.)