The current study examined differences in morphosyntactic knowledge of Arabic learners who had significant exposure to English as a medium of instruction at the primary and tertiary educational levels. The study involved a grammaticality judgment task, an editing task, and a background questionnaire. Based on the background questionnaire, the participants (n = 84) were divided into early and late learners - those first exposed to English medium instruction in the primary and undergraduate levels, respectively. The results of the multivariate analysis revealed a main effect for the age of first exposure to English medium instruction. The post hoc univariate analysis confirmed these effects in favor of early learners only for the grammaticality judgment task; no such effects were observed for the editing task. Theoretical, methodological, and pedagogical implications of the study are discussed.