This study investigates the role of diglossic and orthographic features in reading comprehension in Arabic. Specifically, it probes the independent contribution of language, metalinguistic, and decoding skills in the spoken language and in Standard Arabic to reading comprehension in the "abjad" writing system of Arabic. A sample of 112 Palestinian Arabic native-speaking third graders (mean age = 108.31 months) were tested on receptive vocabulary, phonological awareness, morphological awareness, and word decoding independently in the spoken language and in the standard. Listening comprehension and reading comprehension in the standard were also tested, along with cognitive factors. Regression analysis showed that morphological awareness, receptive vocabulary and decoding accuracy and fluency in the spoken language predicted unique variance in reading comprehension in the standard beyond cognitive ability, with morphological awareness emerging as the strongest predictor. Only decoding accuracy in the standard predicted unique variance in reading comprehension beyond spoken language skills. Listening comprehension entered in the last block contributed a small unique variance. The results underscore the contribution of lexical, metalinguistic, and decoding skills for words within the spoken language to reading comprehension in Standard Arabic. Moreover, they underscore the unique contribution of morphological skills to reading comprehension in the Arabic "abjad" writing system. The results imply that not all of the reading comprehension difficulties that Arabic-speaking children encounter are related to linguistic distance. Rather, some difficulties are grounded in difficulties with basic language, metalinguistic, and decoding skills for words within their spoken vernacular. The implications of these findings for literacy education in Arabic diglossia are discussed.