ABSTRACTSensitivity to differences in lexical stress pattern was examined in 4- and 5-year-old monolingual French-, German- and Swedish-speaking children. For most stimulus discriminations, the 5-year-olds outperformed their 4-year-old comparison groups. For a discrimination involving a trisyllabic distinction not found in French, however, the French 5-year-olds performed worse than their 4-year-old compatriots, suggesting that the older children had ‘learned’ not to hear the trisyllabic distinction. In follow-up testing of the French 4-year-olds six months later, half of them showed a similar decrease in performance specific to the trisyllabic stimuli. These data support an ‘attunement’ theory of language acquisition, in which potentially relevant abilities that are already partially or fully developed at birth may become attenuated or completely lost if they are inappropriate or irrelevant for the child's language.