“…What is especially remarkable in the context of HL acquisition is that aspects of language usually acquired early by monolingual children may show a protracted developmental pattern in child HSs. The acquisition of inflectional morphology, in particular, such as case marking, has been reported as problematic for adult HSs from a range of typologically different languages: from East-Asian languages that allow for case drop (e.g., Korean, Japanese; Kim, O'Grady, & Schwartz, 2017;Laleko & Polinsky, 2016), to Indo-European languages, where a default or a syncretic case is produced (e.g., Russian or German; Laleko & Polinsky, 2016;Montrul, Bhatia, Bhatt, & Puri, 2019). These issues have been shown to emerge in the speech of HL children (Flores, 2015;Janssen, 2017;Janssen, Meir, Baker, & Armon-lotem, 2014;Kim et al, 2017;Song, O'Grady, Cho, & Lee, 1997) 1 and to persist in adult HSs (see Montrul, 2015).…”