Variation along the referentiality scale in the production of Spanish differential object marking by monolingual and bilingual children

Differential object marking (DOM) is the overt marking of prominent direct objects. Heritage speakers of Spanish significantly omit the marker “a” with human/animate objects compared to bilingual Spanish-dominant adults and monolingual child and adult Spanish speakers. This study digs deeper into the high omission rates attested in heritage speakers to uncover what may underlie the observed variability. The diachronic evolution of Spanish DOM followed the referentiality scale, which considers the referential prominence of different object DPs (pronoun, name, definite DP, possessive, quantifier, indefinite DP). We hypothesized that such scale may underlie some patterns of variation. Results of two oral production tasks with school-age Spanish–English bilingual children (n = 61), bilingual adults (n = 12), and monolingual Spanish-speaking children (n = 26) and adults (n = 26) found that while the monolingual children and adults and the bilingual adults showed clear DOM variability along the referentiality scale with animate/human objects, the bilingual children attending school in English in the US and L2 children in bilingual schools in general did not. However, those bilingual children attending dual immersion schools showed an emergent pattern of variability attested in monolingually raised children and adults. Our study confirms that quantity and quality of input, including schooling, matters greatly for heritage language development.