Previous studies in the acquisition of clitic se in Spanish have focused on the syntactic processes needed to perform detransitivization. However, current approaches on event structure reveal that "se" encodes aspectual information which is crucial for its acquisition. We examine the use, intuition and interpretation of the aspectual features constraining the clitic se in Spanish with physical change of state verbs and psychological verbs in declarative sentences, and in a set of "why"-questions. Twenty Spanish heritage speakers (HSs), 20 English-speaking L2 learners of Spanish, and 20 Spanish monolingual speakers participated in the study. Results showed a clear advantage among the HSs over the L2 learners across conditions. In general, the use of se with change of state verbs at advanced levels of proficiency seems to be harder to acquire than with psych verbs due to the aspectual morphological marking in L1 English. Interestingly, L2 learners and HSs were less sensitive to the [+inchoative] feature with psych verbs in "why"-questions. Results are also discussed in terms of the age of onset of bilingualism as an affecting factor on the acquisition of the aspectual values of inchoative "se."