There are differences and similarities between Modern Standard Arabic (MSA) and spoken varieties of Arabic, in all language domains. To obtain preliminary insights into interactions between the acquisition of spoken and standard varieties of a language in a diglossic situation, we employed forced-choice grammaticality judgments to investigate morphosyntactic knowledge of MSA and the local variant of Palestinian Colloquial Arabic (PCA), in 60 Arabic-speaking children aged 6 ; 4 to 12 ; 4, from a school in Nazareth. We used morphosyntactic structures which either differed or were similar between PCA and standard Arabic. Children generally performed better on items presented in PCA than in standard Arabic, with the exception of constructions involving negation. Children performed better on items when the two constructions were similar in both language varieties. We discuss the results with respect to the multiple factors that affect acquisition in a diglossic situation, and relate our findings to the possibility of interference effects of diglossia on learning.