This preliminary study investigates the acquisition of second language phonology with respect to two variables: immersion in a target language community, and explicit instruction in the form of a phonetics/pronunciation class. Specifically, the research examines the second language acquisition (SLA) of specific properties of the Spanish phonology system as achieved by native speakers of English participating in a summer program in Mexico, some of whom had previously taken a Spanish phonetics course. Results suggest that it is not one factor or another in isolation that is most beneficial, but rather the combination of the two. The findings are analyzed not only in terms of how the SLA of sound systems develops, but also with respect to pedagogical, curricular, and administrative implications. (Contains 6 notes, 3 tables, and 1 figure.)