Purpose: The aim of the study was to investigate the effects of specific acoustic patterns on word learning and segmentation in 8- to 11-year-old children and in college students. Method: Twenty-two children (ages 8;2-11;4 [years;months]) and 36 college students listened to synthesized "utterances" in artificial languages consisting of six iterated "words," which followed either a phonetically natural lenition--fortition pattern or an unnatural (cross-linguistically unattested) antilenition pattern. A two-alternative forced-choice task tested whether they could discriminate between occurring and nonoccurring sequences. Participants were exposed to both languages, counterbalanced for order across subjects, in sessions spaced at least 1 month apart. Results: Children showed little evidence for learning in either the phonetically natural or unnatural condition nor evidence of differences in learning across the two conditions. Adults showed the predicted (and previously attested) interaction between learning and phonetic condition: The phonetically natural language was learned better. The adults also showed a strong effect of session: Subjects performed much worse during the second session than the first. Conclusions: School-age children not only failed to demonstrate the phonetic asymmetry demonstrated by adults in previous studies but also failed to show strong evidence for any learning at all. The fact that the phonetic asymmetry (and general learning effect) was replicated with adults suggests that the child result is not due to inadequate stimuli or procedures. The strong carryover effect for adults also suggests that they retain knowledge about the sound patterns of an artificial language for over a month, longer than has been reported in laboratory studies of purely phonetic/phonological learning.