This study tests the hypothesis that late first-language English / second-language Spanish learners (L1 English / L2 Spanish learners) acquire spirantization in stages according to the prosodic hierarchy (Zampini, 1997, 1998). In Spanish, voiced stops [b d g] surface after a pause or nasal stop, and continuants [ß? ð? ??] surface postvocalically, among other contexts. We adopt an Optimality Theoretic analysis of the phenomenon that assumes that postvocalic continuants surface due to the ranking of prosodic positional faithfulness constraints below a markedness constraint that prohibits stops in postvocalic position. L1 English speakers are presumed to start with a ranking in which prosodic positional faithfulness outranks the markedness constraint. In line with the Gradual Learning Algorithm (Boersma and Hayes, 2001), gradual demotion of the relevant faithfulness constraints is predicted in L2 Spanish, extending the prosodic domain until continuants surface postvocalically across domains. A cross-section of 44 L1 English/L2 Spanish learners and a control group (n = 5) completed a recitation task, and data were analysed acoustically for manner of articulation and degree of constriction. Results partially align with Zampini's impressionistic data: Learners first produce underlying stops as postvocalic approximants at the onset of the syllable (word-medial position), followed by the onset of the prosodic word (word-initial position). Unlike Zampini's findings, there is no evidence for an intermediate stage of acquisition across the boundary of a word and its clitic. Advanced L2 learners produce continuants in postvocalic position at all applicable prosodic levels, which we take to indicate acquisition of the target ranking. We also examined whether learners' postvocalic continuants are lenited to the same degree as the control group, and whether degree of lenition changes across development. The difference in degree of lenition between controls and learners lessens at higher levels of the prosodic hierarchy as acquisition progresses, and several advanced learners produce target-like segments across prosodic levels.