The study tested the effect of three factors on Arab children's (N = 256) phoneme isolation: "phoneme's linguistic affiliation" (standard phonemes vs. spoken phonemes), phoneme position (initial vs. final), and linguistic context (singleton vs. cluster). Two groups of children speaking two different vernaculars were tested. The two vernaculars differed with respect to whether they included four critical Standard Arabic phonemes. Using a repeated-measure design, we tested children's phonemic sensitivity toward these four phonemes versus other phonemes. The results showed that the linguistic affiliation of the phoneme was reliable in explaining phoneme isolation reaffirming, hence the external validity of the "linguistic affiliation constraint" in explaining phoneme awareness in diglossic Arabic. The results also showed that initial phonemes and initial singleton phonemes were particularly difficult for children to isolate. These findings were discussed in light of a stipulated unique phonological and orthographic cohesion of the consonant-vowel unit in Arabic.