This study of code-mixing focuses on the influence of Spanish in NahuatI discourse as it is revealed in performance in narratives produced by adults and children. Language samples analysed were non-conversational, produced in response to structured NahuatI language story-telling tasks presented to participants. Narrators were bilingual speakers of the two languages from an indigenous community in Central Mexico. Results indicate differences in the frequency of content word embedded language (Spanish) lexical items across grade level (for children), grade level attained (for adults), and correlations (for children) between the frequency of these Spanish embedded items and a measure of metalinguistic awareness. The discussion of findings is placed in the context of a language contact situation characterised by the rapid shift toward Spanish mOnolingualism in the broader surrounding region (Tlaxcalan Highlands) despite high levels of NahuatI language proficiency in the locality in which the study was carried out.