This study examines the variable occurrence of preposition duplication in contexts of coordination in Spanish (e.g., "Fui con mi madre y (con) mi padre"). We build on previous research on this variable morphosyntactic phenomenon (namely, prepositions in contexts of coordination) by expanding the type of data and the independent variables analyzed. The examination of data from a written contextualized task suggests that duplication is the preferred variant for native speakers and that the linguistic factors of animacy, preposition type, and coordinator condition variation. We also extend the investigation of prepositions in contexts of coordination to adult second-language learners of Spanish. The results from four instructional levels of learners show numerous changes along the acquisitional path, both in the frequency of selection of the variants and of the factors that predict their occurrence. They also suggest that this variable structure is acquired late. Thus, the present investigation contributes to the understanding of second-language variation by providing information on the developmental trajectory and targetlikeness of a variable structure that has not been examined previously in the field of second language acquisition.