The current study attempted to investigate academic vocabulary knowledge in middle school in the shadows of diglossic Arabic, affecting the ability to cope with informational texts. For this purpose, 1,322 Arabic native speaking middle school pupils participated in this study, representing the different subgroups of the Arab minority in Israel (i.e. general Arab community, Druze community and Bedouin community). Three academic vocabulary measures were developed, examining academic vocabulary declarative knowledge, application of academic vocabulary in context and production of academic vocabulary. Differences in academic vocabulary knowledge were assessed in relation to age group, Arab sub-group affiliation and gender differences. The results pointed to significant differences between the age groups in all the evaluation measures, where 7th graders showed the lowest performance when compared to 8th and 9th grade. In addition, significant differences were obtained between the Arab sub-groups where the lowest performance was noted among the Bedouin community, characterized by lower socio-economic background, where the highest performance was found among the Druze community. In addition, gender differences were encountered, pointing to girls' superiority in performance across all measures and age groups.