The acquisition of the Spanish morpheme se has proved to be problematic for L2 learners both because of its polyfunctionality and because of the restrictions regarding the types of predicates with which it can combine. This paper sheds light on this problem by focusing on a specific type of se (anticausative se; e.g., El jarrón se rompió ‘The vase broke’) and exploring its acquisition across four proficiency levels. Results of a scalar grammaticality judgment task indicate that lower-proficiency participants’ performance is in line with previous research, which claims that this aspect of Spanish grammar is particularly challenging for L2 learners (as reflected in omission and overgeneralization errors). However, the near-native group shows sensitivity to the abstract features that uniquely characterize verbs that undergo the causative/inchoative alternation. Thus, the current findings suggest that L2 learners manage to overcome the problems experienced at lower levels and, in fact, do succeed at the level of ultimate.