AbstractThis study is a cross-sectional developmental investigation of inflectional and derivational morphological awareness (MA) in Arabic diglossia. It examines the impact of the morphological distance between Spoken Arabic (SpA) and Standard Arabic (StA) on inflectional morphological awareness and derivational morphological awareness in a sample of 200 speakers of Palestinian Arabic (PA) in 2nd through 10th grade from mid-high and low SES backgrounds (N = 40 per grade, 20 per SES group). Eight MA tasks using morphological analogies and sentence completion were used that tested inflectional MA and derivational MA in SpA and in StA. Results showed a growth in inflectional and in derivational awareness across grades in both SES groups despite generally higher scores in the mid-high SES group. More interestingly, the results showed a consistent effect of morphological distance on morphological awareness in both morphological systems and in both SES groups, with MA for unique StA morphological structures lower than that for structures available in SpA. Moreover, the impact of morphological distance was more prominent in younger than in older children and in low than in mid-high SES. Finally, when morphological awareness in SpA was tested, inflectional awareness was higher than derivational awareness and showed a shorter cross-sectional developmental trajectory, reflecting universal linguistic and distributional properties of inflections. In contrast, when morphological awareness in StA was analyzed, inflectional awareness was lower than derivational awareness and showed a longer trajectory reflecting the wider linguistic distance between SpA and StA in inflectional morphology. The results underscore the significance of morphological system characteristics and morphological distance in understanding morphological awareness development in Arabic.