Heritage language (HL) learners of Spanish have shown better command with early acquired aspects of grammar than second language (L2) learners, mainly in oral tasks. This study investigates whether this advantage persists with passive clauses, structures acquired early but mastered during the school-age years, with literacy. We examined adjectival passives (La comida estaba servida, “Dinner was served”) with the copula estar in the imperfect, which refer to a description of a state or a final result; and verbal passives with the copula ser in the imperfect (La comida era servida. “Dinner was being served”), which refer to an ongoing or habitual action in the past. A grammaticality judgment task (GJT) testing knowledge of the copulas in different simple sentences and a picture-matching task (PMT) testing the comprehension of the two passive clauses revealed that HL learners’ knowledge of the copulas resembles that of literate monolingually raised native speakers more than that of L2 learners. HL learners are able to integrate their knowledge of the copulas to comprehend syntactically complex clauses, especially in the aural modality.