This study examines the role of language proficiency and other individual factors (attitudes, input) in the acquisition of language-specific [ð] and dialect-specific [Ø] allophones of Spanish intervocalic /d/ in the /ado/ context by L2 and heritage Spanish speakers during a short-term study abroad in Sevilla, Spain. Twenty L2-intermediate, 10 L2-advanced, and 10 Heritage-advanced Spanish speakers completed a reading task at the beginning and the end of the program. Based on an acoustic analysis, a mixed-effects linear regression model found that only L2-advanced and Heritage-advanced groups demonstrated more approximant-like [ð] over time. However, proficiency level interacted with attitudes and input. There were a few [Ø] realizations, mostly produced by an L2-advanced speaker who also demonstrated metalinguistic awareness of the dialect-specific allophone. The findings imply that advanced (L2 and heritage) speakers with favorable attitudes toward the local variety are most likely to demonstrate gradient language-specific allophonic changes during a short-term SA program.